diff --git a/postfix/HISTORY b/postfix/HISTORY index 790ecad50..41a0c3c68 100644 --- a/postfix/HISTORY +++ b/postfix/HISTORY @@ -15080,3 +15080,14 @@ Apologies for any names omitted. compatibility. Adding such headers to remote mail can break DKIM signatures that cover headers that are not present. File: cleanup/cleanup_message.c. + +20090415 + + Workaround: to avoid unnecessary "fatal" delivery agent + exits, delivery agents retry getting a shared lock on a + queue file. This is necessary since the queue manager's + behavior was changed years ago to refill the in-memory + recipient list before it was completely empty. File: + global/deliver_request.c. + + Documentation: updated STRESS_README. diff --git a/postfix/README_FILES/AAAREADME b/postfix/README_FILES/AAAREADME index 31d9c0e58..2dd6cac2b 100644 --- a/postfix/README_FILES/AAAREADME +++ b/postfix/README_FILES/AAAREADME @@ -12,6 +12,7 @@ GGeenneerraall ccoonnffiigguurraattiioonn * TLS_README: TLS Encryption and authentication * TLS_LEGACY_README: Legacy TLS support * IPV6_README: IP Version 6 Support + * MULTI_INSTANCE_README: Multiple-instance management * INSTALL: Installation from source code PPrroobblleemm ssoollvviinngg diff --git a/postfix/README_FILES/SMTPD_POLICY_README b/postfix/README_FILES/SMTPD_POLICY_README index 7ba1838da..a98a675f1 100644 --- a/postfix/README_FILES/SMTPD_POLICY_README +++ b/postfix/README_FILES/SMTPD_POLICY_README @@ -88,9 +88,9 @@ Notes: attribute, sends the attribute with an empty value ("name="), or sends a zero value ("name=0") in the case of a numerical attribute. - * The "recipient" attribute is available only in the "RCPT TO" stage, and in - the "DATA" and "END-OF-MESSAGE" stages when Postfix accepted only one - recipient for the current message. + * The "recipient" attribute is available in the "RCPT TO" stage. It is also + available in the "DATA" and "END-OF-MESSAGE" stages if Postfix accepted + only one recipient for the current message. * The "recipient_count" attribute (Postfix 2.3 and later) is non-zero only in the "DATA" and "END-OF-MESSAGE" stages. It specifies the number of diff --git a/postfix/README_FILES/STRESS_README b/postfix/README_FILES/STRESS_README index ebf3095e8..1e4c3e432 100644 --- a/postfix/README_FILES/STRESS_README +++ b/postfix/README_FILES/STRESS_README @@ -4,12 +4,11 @@ PPoossttffiixx SSttrreessss--DDeeppeennddeenntt CCoonn OOvveerrvviieeww -This document describes the symptoms of Postfix SMTP server overload, and how -to avoid the condition under normal conditions. When the condition is caused by -botnets or other malware, the document suggests configuration settings that -help to minimize the impact on legitimate mail. Finally, the document -introduces stress-adaptive behavior, introduced with Postfix 2.5, and how it -can be used to automatically switch configuration settings under overload. +This document describes the symptoms of Postfix SMTP server overload. It +presents permanent main.cf changes to avoid overload during normal operation, +and temporary main.cf changes to cope with an unexpected burst of mail. This +document makes specific suggestions for Postfix 2.5 and later which support +stress-adaptive behavior, and for earlier Postfix versions that don't. Topics covered in this document: @@ -17,42 +16,46 @@ Topics covered in this document: * Service more SMTP clients at the same time * Spend less time per SMTP client * Disconnect suspicious SMTP clients - * Take desperate measures - * Make Postfix behavior stress-adaptive + * Temporary measures for older Postfix releases + * Automatic stress-adaptive behavior * Detecting support for stress-adaptive behavior * Forcing stress-adaptive behavior on or off + * Other measures to off-load zombies * Credits SSyymmppttoommss ooff PPoossttffiixx SSMMTTPP sseerrvveerr oovveerrllooaadd -Under normal conditions, Postfix responds immediately when a remote SMTP client -connects. The time needed to deliver mail should be noticeable only with very -large messages. Performance degrades more dramatically when the number of -remote SMTP clients exceeds the number of Postfix SMTP server processes. When a -client connects while all server processes are busy, the client must wait until -a server process becomes available. +Under normal conditions, the Postfix SMTP server responds immediately when an +SMTP client connects to it; the time to deliver mail is noticeable only with +large messages. Performance degrades dramatically when the number of SMTP +clients exceeds the number of Postfix SMTP server processes. When an SMTP +client connects while all Postfix SMTP server processes are busy, the client +must wait until a server process becomes available. -Overload may be caused by a legitimate mail (example: a DNS registrar opens a -new zone for registrations), by mistake (mail explosion caused by a forwarding -loop) or by illegitimate mail (worm outbreak, botnet, or other malware -activity). Symptoms of Postfix SMTP mail server overload are: +SMTP server overload may be caused by a surge of legitimate mail (example: a +DNS registrar opens a new zone for registrations), by mistake (mail explosion +caused by a forwarding loop) or by malice (worm outbreak, botnet, or other +illegitimate activity). + +Symptoms of Postfix SMTP server overload are: * Remote SMTP clients experience a long delay before Postfix sends the "220 - hostname.example.com ESMTP Postfix" greeting. If this affects end-user mail - clients, enable the "submission" service entry in master.cf (present since - Postfix 2.1), and tell users to connect to this instead of the public SMTP - service. + hostname.example.com ESMTP Postfix" greeting. - o NOTE: Broken DNS configurations also cause lengthy delays before - Postfix sends "220 hostname.example.com ...". In this case the delay - happens even when Postfix is not busy. + o NOTE: Broken DNS configurations can also cause lengthy delays before + Postfix sends "220 hostname.example.com ...". These delays also exist + when Postfix is NOT overloaded. + + o NOTE: To avoid "overload" delays for end-user mail clients, enable the + "submission" service entry in master.cf (present since Postfix 2.1), + and tell users to connect to this instead of the public SMTP service. * The Postfix SMTP server logs an increased number of "lost connection after CONNECT" events. This happens because remote SMTP clients disconnect before Postfix answers the connection. - o NOTE: A portscan for open SMTP ports also results in "lost connection - ..." logfile messages. + o NOTE: A portscan for open SMTP ports can also result in "lost + connection ..." logfile messages. * Postfix 2.3 and later logs a warning that all server ports are busy: @@ -63,15 +66,16 @@ activity). Symptoms of Postfix SMTP mail server overload are: condition, increase the process count in master.cf or reduce the service time per client -Legitimate mail that doesn't get through during an episode of overload is not -necessarily lost. It should still arrive once the situation returns to normal, -as long as the overload condition is temporary. +Legitimate mail that doesn't get through during an episode of Postfix SMTP +server overload is not necessarily lost. It should still arrive once the +situation returns to normal, as long as the overload condition is temporary. SSeerrvviiccee mmoorree SSMMTTPP cclliieennttss aatt tthhee ssaammee ttiimmee -To service more SMTP clients simultaneously, you need to increase the number of -SMTP server processes. This will improve the responsiveness for remote SMTP -clients, as long as the server machine has enough hardware and software +One measure to avoid the "all server processes busy" condition is to service +more SMTP clients simultaneously. For this you need to increase the number of +Postfix SMTP server processes. This will improve the responsiveness for remote +SMTP clients, as long as the server machine has enough hardware and software resources to run the additional processes, and as long as the file system can keep up with the additional load. @@ -84,8 +88,9 @@ keep up with the additional load. operating system that supports kernel-based event filters (BSD kqueue(2), Linux epoll(4), or Solaris /dev/poll). - * You can reduce the Postfix memory footprint by using cdb: lookup tables - instead of Berkeley DB's hash: or btree: tables. + * More processes use more memory. You can reduce the Postfix memory footprint + by using cdb: lookup tables instead of Berkeley DB's hash: or btree: + tables. 1 /etc/postfix/main.cf: 2 # Raise the global process limit, 100 since Postfix 2.0. @@ -120,9 +125,9 @@ keep up with the additional load. SSppeenndd lleessss ttiimmee ppeerr SSMMTTPP cclliieenntt When increasing the number of SMTP server processes is not practical, you can -improve Postfix server responsiveness by eliminating unnecessary work. When -Postfix spends less time per SMTP session, the same number of SMTP server -processes can service more clients in the same amount of time. +improve Postfix server responsiveness by eliminating delays. When Postfix +spends less time per SMTP session, the same number of SMTP server processes can +service more clients in a given amount of time. * Eliminate non-functional RBL lookups (blocklists that are no longer in operation). These lookups can degrade performance. Postfix logs a warning @@ -137,18 +142,18 @@ processes can service more clients in the same amount of time. BACKSCATTER_README for examples of the latter. * Group your header_checks and body_checks patterns to avoid unnecessary - pattern matching operations. + pattern matching operations: 1 /etc/postfix/header_checks: 2 if /^Subject:/ 3 /^Subject: virus found in mail from you/ reject - 4 /^Subject: ..../ .... + 4 /^Subject: ..other../ reject 5 endif 6 7 if /^Received:/ 8 /^Received: from (postfix\.org) / reject forged client name in received header: $1 - 9 /^Received: from .../ .... + 9 /^Received: from ..other../ reject .... 10 endif DDiissccoonnnneecctt ssuussppiicciioouuss SSMMTTPP cclliieennttss @@ -157,14 +162,16 @@ Under conditions of overload you can improve Postfix SMTP server responsiveness by hanging up on suspicious clients, so that other clients get a chance to talk to Postfix. - * Use "521" reply codes (Postfix 2.6 and later) for botnet-related RBLs or - for selected non-RBL restrictions. With Postfix 2.3-2.5 use "421" for a - similar result. The Postfix SMTP server will disconnect immediately without + * Use "521" SMTP reply codes (Postfix 2.6 and later) or "421" (Postfix 2.3- + 2.5) to hang up on clients that that match botnet-related RBLs (see next + bullet) or that match selected non-RBL restrictions such as SMTP access + maps. The Postfix SMTP server will reject mail and disconnect without waiting for the remote SMTP client to send a QUIT command. - You can set individual reject codes for RBLs, and for individual responses - from a specific RBL. We'll use zen.spamhaus.org as an example; by the time - you read this document, details may have changed. Right now, their + * To hang up connections from blacklisted zombies, you can set specific + Postfix SMTP server reject codes for specific RBLs, and for individual + responses from specific RBLs. We'll use zen.spamhaus.org as an example; by + the time you read this document, details may have changed. Right now, their documents say that a response of 127.0.0.10 or 127.0.0.11 indicates a dynamic client IP address, which means that the machine is probably running a bot of some kind. To give a 521 response instead of the default 554 @@ -180,37 +187,45 @@ to Postfix. 8 rbl_reply_maps = hash:/etc/postfix/rbl_reply_maps 9 10 /etc/postfix/rbl_reply_maps: - 11 zen.spamhaus.org=127.0.0.10 521 4.7.1 Service unavailable; - 12 $rbl_class [$rbl_what] blocked using - 13 $rbl_domain${rbl_reason?; $rbl_reason} - 14 - 15 zen.spamhaus.org=127.0.0.11 521 4.7.1 Service unavailable; - 16 $rbl_class [$rbl_what] blocked using - 17 $rbl_domain${rbl_reason?; $rbl_reason} + 11 # With Postfix 2.3-2.5 use "421" to hang up connections. + 12 zen.spamhaus.org=127.0.0.10 521 4.7.1 Service unavailable; + 13 $rbl_class [$rbl_what] blocked using + 14 $rbl_domain${rbl_reason?; $rbl_reason} + 15 + 16 zen.spamhaus.org=127.0.0.11 521 4.7.1 Service unavailable; + 17 $rbl_class [$rbl_what] blocked using + 18 $rbl_domain${rbl_reason?; $rbl_reason} - Although the above shows three RBL lookups (lines 4-6), Postfix will still - only do a single DNS query, so the performance difference is negligible. + Although the above example shows three RBL lookups (lines 4-6), Postfix + will only do a single DNS query, so it does not affect the performance. - With Postfix 2.3-2.5, use 421 (reply code 521 will not cause Postfix to - disconnect). The down-side of sending 421 is that it works only for zombies - and other malware. If the client is running a real MTA, then it may connect - again several times until the mail expires in its queue. When this is a - problem, stick with the default 554 reply, and use "smtpd_hard_error_limit - = 1" as described below. + * With Postfix 2.3-2.5, use reply code 421 (521 will not cause Postfix to + disconnect). The down-side of replying with 421 is that it works only for + zombies and other malware. If the client is running a real MTA, then it may + connect again several times until the mail expires in its queue. When this + is a problem, stick with the default 554 reply, and use + "smtpd_hard_error_limit = 1" as described below. - With Postfix 2.5, or with earlier releases that contain the stress-adaptive - behavior patch, you can turn on the above under overload by replacing line - 8 with: + * You can automatically turn on the above overload measure with Postfix 2.5 + and later, or with earlier releases that contain the stress-adaptive + behavior source code patch from the mirrors listed at http:// + www.postfix.org/download.html. Simply replace line above 8 with: 8 rbl_reply_maps = ${stress?hash:/etc/postfix/rbl_reply_maps} - More information about automatic stress-adaptive behavior is at the end of - this document. +More information about automatic stress-adaptive behavior is in section +"Automatic stress-adaptive behavior". -TTaakkee ddeessppeerraattee mmeeaassuurreess +TTeemmppoorraarryy mmeeaassuurreess ffoorr oollddeerr PPoossttffiixx rreelleeaasseess -The following measures will still allow mmoosstt legitimate clients to connect and -send mail, but may affect some legitimate clients. +See the next section, "Automatic stress-adaptive behavior", if you are running +Postfix version 2.5 or later, or if you have applied the source code patch for +stress-adaptive behavior from the mirrors listed at http://www.postfix.org/ +download.html. + +The following measures can be applied temporarily during overload. They still +allow mmoosstt legitimate clients to connect and send mail, but may affect some +legitimate clients. * Reduce smtpd_timeout (default: 300s). Experience on the postfix-users list from a variety of sysadmins shows that reducing the "normal" smtpd_timeout @@ -228,55 +243,75 @@ send mail, but may affect some legitimate clients. longer-active user names that didn't bother to unsubscribe. No mail should be lost, as long as this measure is used only temporarily. - * Disable remote SMTP client hostname lookups, so that all SMTP client - hostnames become "unknown" (line 5 below). This feature was introduced with - Postfix 2.3. Unfortunately, this measure is more problematic than the other - ones proposed sofar. First, this will result in loss of mail when you use - hostname-based access rules that reject mail from "unknown" SMTP clients - (examples: reject_unknown_client_hostname, - reject_unknown_reverse_client_hostname). Second, this may result in loss of - mail when you subject "unknown" SMTP clients to additional restrictions - such as reject_unverified_sender. + * Use an smtpd_junk_command_limit of 1 instead of the default 100. This + prevents clients from keeping idle connections open by repeatedly sending + NOOP or RSET commands. 1 /etc/postfix/main.cf: 2 smtpd_timeout = 10 3 smtpd_hard_error_limit = 1 - 4 # Caution: line 5 may trigger REJECTs by hostname-based access rules + 4 smtpd_junk_command_limit = 1 - 5 smtpd_peername_lookup = no +With these measures, no mail should be lost, as long as these measures are used +only temporarily. The next section of this document introduces a way to +automate this process. -Except with the last measure, no mail should be lost, as long as these measures -are used only temporarily. The next section of this document introduces a way -to automate this process. - -MMaakkee PPoossttffiixx bbeehhaavviioorr ssttrreessss--aaddaappttiivvee +AAuuttoommaattiicc ssttrreessss--aaddaappttiivvee bbeehhaavviioorr Postfix version 2.5 introduces automatic stress-adaptive behavior. This is also -available as an add-on patch for Postfix versions 2.4 and 2.3 from the mirrors -listed at http://www.postfix.org/download.html. +available as a source code patch for Postfix versions 2.4 and 2.3 from the +mirrors listed at http://www.postfix.org/download.html. -It works as follows. When a "public" network service runs into an "all server -ports are busy" condition, the master(8) daemon logs a warning, restarts the -service (without interrupting existing network sessions), and runs the service -with "-o stress=yes" on the command line. Normally, it runs a stress-adaptive -service with "-o stress=" on the command line (i.e. with an empty parameter -value). Other services never have "-o stress" parameters on the command line, -including services that listen on a loopback interface only. +It works as follows. When a "public" network service such as the SMTP server +runs into an "all server ports are busy" condition, the Postfix master(8) +daemon logs a warning, restarts the service (without interrupting existing +network sessions), and runs the service with "-o stress=yes" on the server +process command line: -The stress pseudo-parameter value is the key to making main.cf parameter -settings stress adaptive: + 80821 ?? S 0:00.24 smtpd -n smtp -t inet -u -c -o stress=yes - 1 /etc/postfix/main.cf: - 2 smtpd_timeout = ${stress?10}${stress:300} - 3 smtpd_hard_error_limit = ${stress?1}${stress:20} +Normally, the Postfix master(8) daemon runs such a service with "-o stress=" on +the command line (i.e. with an empty parameter value): + + 83326 ?? S 0:00.28 smtpd -n smtp -t inet -u -c -o stress= + +Services that have local access only never have "-o stress" parameters on the +command line. This includes services internal to Postfix such as the queue +manager, and services that listen on a loopback interface only, such as after- +filter SMTP services. + +The "stress" parameter value is the key to making main.cf parameter settings +stress adaptive. The following settings are the default with Postfix 2.6 and +later. With earlier Postfix versions that have stress-adaptive support, append +the lines below to the main.cf file and issue a "postfix reload" command: + + 1 smtpd_timeout = ${stress?10}${stress:300}s + 2 smtpd_hard_error_limit = ${stress?1}${stress:20} + 3 smtpd_junk_command_limit = ${stress?1}${stress:100} Translation: - * Line 2: under conditions of stress, use an smtpd_timeout value of 10 - seconds instead of the default 300 seconds, + * Line 1: under conditions of stress, use an smtpd_timeout value of 10 + seconds instead of the default 300 seconds. Experience on the postfix-users + list from a variety of sysadmins shows that reducing the "normal" + smtpd_timeout to 60s is unlikely to affect legitimate clients. However, it + is unlikely to become the Postfix default because it's not RFC compliant. + Setting smtpd_timeout to 10s (line 2 below) or even 5s under stress will + still allow most legitimate clients to connect and send mail, but may delay + mail from some clients. No mail should be lost, as long as this measure is + used only temporarily. - * Line 3: under conditions of stress, use an smtpd_hard_error_limit of 1 - instead of the default 20. + * Line 2: under conditions of stress, use an smtpd_hard_error_limit of 1 + instead of the default 20. This helps by disconnecting clients after a + single error, giving other clients a chance to connect. However, this may + cause significant delays with legitimate mail, such as a mailing list that + contains a few no-longer-active user names that didn't bother to + unsubscribe. No mail should be lost, as long as this measure is used only + temporarily. + + * Line 3: under conditions of stress, use an smtpd_junk_command_limit of 1 + instead of the default 100. This prevents clients from keeping idle + connections open by repeatedly sending NOOP or RSET commands. The syntax of ${name?value} and ${name:value} is explained at the beginning of the postconf(5) manual page. @@ -346,6 +381,18 @@ accept remote connections. 7 -o stress= 8 -o . . . +OOtthheerr mmeeaassuurreess ttoo ooffff--llooaadd zzoommbbiieess + +OpenBSD spamd implements a daemon that handles all connections from "new" +clients. Only well-behaved mail clients are allowed to talk to the mail server. +Other clients are tarpitted, and will never get a chance to affect mail server +performance. + +At some point in the future, Postfix may come with a simple front-end daemon +that does basic greylisting and pipelining detection to keep zombies and other +ratware away from Postfix itself. This would use the "pass" service type which +has been available in stable Postfix releases since Postfix 2.5. + CCrreeddiittss * Thanks to the postfix-users mailing list members for sharing early diff --git a/postfix/WISHLIST b/postfix/WISHLIST index 84f31dd8b..48652ee1b 100644 --- a/postfix/WISHLIST +++ b/postfix/WISHLIST @@ -9,25 +9,18 @@ Wish list: compatibility. The "first" setting is good for performance (stress=yes) when all users are defined in local files. - Make the double-bounce address time-dependent (with 24-hour - grace period). Spammers appear to use this address to avoid - DATA command rejects. Avoiding DATA rejects means they can - pipeline the entire SMTP session without triggering huge - numbers of protocol errors. They can still trigger "improper - command pipelining after DATA" alarms, but that requires - non-default main.cf settings. - Cleanup: make DNSBL query format configurable beyond the client's reversed IP address. With 'final delivery' in the LMTP client, need an option - to also add delivered-to and other pipe(8) features. - This requires making mail_copy() more generic. + to also add delivered-to and other pipe(8) features. This + requires making mail_copy() functionality available in + non-mailbox context. To work around historical AWK's limit of 10 open files, pipe all output into a shell and have the shell open files. - It's too much pain to find out whose AWK is old and where - if any they keep the XPG4 compliant version. + It's too much pain to find out what systems use ancient AWK + and where, if any, they keep the XPG4 compliant version. Cleanup: modernize the "add missing From: header" code, to ``phrase '' form. Most likely, quote the entire phrase diff --git a/postfix/html/SMTPD_POLICY_README.html b/postfix/html/SMTPD_POLICY_README.html index fef97a1ac..42c3e2f4e 100644 --- a/postfix/html/SMTPD_POLICY_README.html +++ b/postfix/html/SMTPD_POLICY_README.html @@ -126,10 +126,10 @@ stress= an empty value ("name="), or sends a zero value ("name=0") in the case of a numerical attribute.

-

  • The "recipient" attribute is available only in the - "RCPT TO" stage, and in the "DATA" and "END-OF-MESSAGE" stages - when Postfix accepted only one recipient for the current message. -

    +

  • The "recipient" attribute is available in the "RCPT + TO" stage. It is also available in the "DATA" and "END-OF-MESSAGE" + stages if Postfix accepted only one recipient for the current + message.

  • The "recipient_count" attribute (Postfix 2.3 and later) is non-zero only in the "DATA" and "END-OF-MESSAGE" stages. It diff --git a/postfix/html/STRESS_README.html b/postfix/html/STRESS_README.html index 0a090a2c3..49a99408f 100644 --- a/postfix/html/STRESS_README.html +++ b/postfix/html/STRESS_README.html @@ -21,13 +21,11 @@ Stress-Dependent Configuration

    Overview

    This document describes the symptoms of Postfix SMTP server -overload, and how to avoid the condition under normal conditions. -When the condition is caused by botnets or other malware, the -document suggests configuration settings that help to minimize the -impact on legitimate mail. Finally, the document introduces -stress-adaptive behavior, introduced with Postfix 2.5, and how it -can be used to automatically switch configuration settings under -overload.

    +overload. It presents permanent main.cf changes to avoid overload +during normal operation, and temporary main.cf changes to cope with +an unexpected burst of mail. This document makes specific suggestions +for Postfix 2.5 and later which support stress-adaptive behavior, +and for earlier Postfix versions that don't.

    Topics covered in this document:

    @@ -41,47 +39,52 @@ overload.

  • Disconnect suspicious SMTP clients -
  • Take desperate measures +
  • Temporary measures for older Postfix releases -
  • Make Postfix behavior stress-adaptive +
  • Automatic stress-adaptive behavior
  • Detecting support for stress-adaptive behavior
  • Forcing stress-adaptive behavior on or off +
  • Other measures to off-load zombies +
  • Credits

    Symptoms of Postfix SMTP server overload

    -

    Under normal conditions, Postfix responds immediately when a -remote SMTP client connects. The time needed to deliver mail should -be noticeable only with very large messages. Performance degrades -more dramatically when the number of remote SMTP clients exceeds -the number of Postfix SMTP server processes. When a client connects -while all server processes are busy, the client must wait until a -server process becomes available.

    +

    Under normal conditions, the Postfix SMTP server responds +immediately when an SMTP client connects to it; the time to deliver +mail is noticeable only with large messages. Performance degrades +dramatically when the number of SMTP clients exceeds the number of +Postfix SMTP server processes. When an SMTP client connects while +all Postfix SMTP server processes are busy, the client must wait +until a server process becomes available.

    -

    Overload may be caused by a legitimate mail (example: a DNS -registrar opens a new zone for registrations), by mistake (mail -explosion caused by a forwarding loop) or by illegitimate mail (worm -outbreak, botnet, or other malware activity). Symptoms of Postfix -SMTP mail server overload are:

    +

    SMTP server overload may be caused by a surge of legitimate +mail (example: a DNS registrar opens a new zone for registrations), +by mistake (mail explosion caused by a forwarding loop) or by malice +(worm outbreak, botnet, or other illegitimate activity).

    + +

    Symptoms of Postfix SMTP server overload are:

    Legitimate mail that doesn't get through during an episode of -overload is not necessarily lost. It should still arrive once the -situation returns to normal, as long as the overload condition is -temporary.

    +Postfix SMTP server overload is not necessarily lost. It should +still arrive once the situation returns to normal, as long as the +overload condition is temporary.

    Service more SMTP clients at the same time

    -

    To service more SMTP clients simultaneously, you need to increase -the number of SMTP server processes. This will improve the +

    One measure to avoid the "all server processes busy" condition +is to service more SMTP clients simultaneously. For this you need +to increase the number of Postfix SMTP server processes. This will +improve the responsiveness for remote SMTP clients, as long as the server machine has enough hardware and software resources to run the additional processes, and as long as the file system can keep up with the @@ -137,7 +142,8 @@ later, and an operating system that supports kernel-based event filters (BSD kqueue(2), Linux epoll(4), or Solaris /dev/poll).

    -

  • You can reduce the Postfix memory footprint by using cdb: +

  • More processes use more memory. You can reduce the Postfix +memory footprint by using cdb: lookup tables instead of Berkeley DB's hash: or btree: tables. 

    @@ -181,9 +187,9 @@ Issue a "postfix reload" command to make the change effective.  
    
 
 
     When increasing the number of SMTP server processes is not
 practical, you can improve Postfix server responsiveness by eliminating
-unnecessary work. When Postfix spends less time per SMTP session, the
-same number of SMTP server processes can service more clients in the
-same amount of time. 
    
+delays.  When Postfix spends less time per SMTP session, the same
+number of SMTP server processes can service more clients in a given
+amount of time. 
    
 
 
      
 
@@ -201,18 +207,18 @@ emergency patterns to block the latest worm explosion or backscatter
 mail.  See BACKSCATTER_README for examples of the latter.
 
 
    •  
       Group your header_checks and body_checks patterns to avoid
-unnecessary pattern matching operations.
+unnecessary pattern matching operations:
 
 
        1  /etc/postfix/header_checks:
  2      if /^Subject:/
  3      /^Subject: virus found in mail from you/ reject
- 4      /^Subject: ..../ ....
+ 4      /^Subject: ..other../ reject
  5      endif
  6  
  7      if /^Received:/
  8      /^Received: from (postfix\.org) / reject forged client name in received header: $1
- 9      /^Received: from .../ ....
+ 9      /^Received: from ..other../ reject ....
 10      endif
 
      
 
@@ -226,20 +232,22 @@ clients get a chance to talk to Postfix.  
      
 
 
        
 
-
      •  
         Use "521" reply codes (Postfix 2.6 and later) for
-botnet-related RBLs or for selected non-RBL restrictions. With
-Postfix 2.3-2.5 use "421" for a similar result. The Postfix SMTP
-server will disconnect immediately without waiting for the remote
-SMTP client to send a QUIT command. 
        
+
      •  
         Use "521" SMTP reply codes (Postfix 2.6 and later) or "421"
+(Postfix 2.3-2.5) to hang up on clients that that match botnet-related
+RBLs (see next bullet) or that match selected non-RBL restrictions
+such as SMTP access maps.  The Postfix SMTP server will reject mail
+and disconnect without waiting for the remote SMTP client to send
+a QUIT command.  
        
 
-
         You can set individual reject codes for RBLs, and for individual
-responses from a specific RBL. We'll use zen.spamhaus.org as an
-example; by the time you read this document, details may have
-changed.  Right now, their documents say that a response of 127.0.0.10
-or 127.0.0.11 indicates a dynamic client IP address, which means
-that the machine is probably running a bot of some kind.  To give
-a 521 response instead of the default 554 response, use something
-like: 
        
+
      •  
         To hang up connections from blacklisted zombies, you can
+set specific Postfix SMTP server reject codes for specific RBLs,
+and for individual responses from specific RBLs. We'll use
+zen.spamhaus.org as an example; by the time you read this document,
+details may have changed.  Right now, their documents say that a
+response of 127.0.0.10 or 127.0.0.11 indicates a dynamic client IP
+address, which means that the machine is probably running a bot of
+some kind.  To give a 521 response instead of the default 554
+response, use something like: 
        
 
 
          1  /etc/postfix/main.cf:
@@ -252,45 +260,55 @@ like: 
        
  8      rbl_reply_maps = hash:/etc/postfix/rbl_reply_maps
  9  
 10  /etc/postfix/rbl_reply_maps:
-11      zen.spamhaus.org=127.0.0.10 521 4.7.1 Service unavailable;
-12       $rbl_class [$rbl_what] blocked using
-13       $rbl_domain${rbl_reason?; $rbl_reason}
-14  
-15      zen.spamhaus.org=127.0.0.11 521 4.7.1 Service unavailable;
-16       $rbl_class [$rbl_what] blocked using
-17       $rbl_domain${rbl_reason?; $rbl_reason}
+11      # With Postfix 2.3-2.5 use "421" to hang up connections.
+12      zen.spamhaus.org=127.0.0.10 521 4.7.1 Service unavailable;
+13       $rbl_class [$rbl_what] blocked using
+14       $rbl_domain${rbl_reason?; $rbl_reason}
+15  
+16      zen.spamhaus.org=127.0.0.11 521 4.7.1 Service unavailable;
+17       $rbl_class [$rbl_what] blocked using
+18       $rbl_domain${rbl_reason?; $rbl_reason}
 
        
 
-
         Although the above shows three RBL lookups (lines 4-6), Postfix
-will still only do a single DNS query, so the performance difference
-is negligible. 
        
+
         Although the above example shows three RBL lookups (lines 4-6),
+Postfix will only do a single DNS query, so it does not affect the
+performance. 
        
 
-
         With Postfix 2.3-2.5, use 421 (reply code 521 will not cause
-Postfix to disconnect). The down-side of sending 421 is that
-it works only for zombies and other malware. If the client is running
-a real MTA, then it may connect again several times until the mail
-expires in its queue. When this is a problem, stick with the default
-554 reply, and use "smtpd_hard_error_limit = 1" as described below.
-
        
+
      •  
         With Postfix 2.3-2.5, use reply code 421 (521 will not
+cause Postfix to disconnect). The down-side of replying with 421
+is that it works only for zombies and other malware. If the client
+is running a real MTA, then it may connect again several times until
+the mail expires in its queue. When this is a problem, stick with
+the default 554 reply, and use "smtpd_hard_error_limit = 1" as
+described below.  
        
 
-
         With Postfix 2.5, or with earlier releases that contain the
-stress-adaptive behavior patch, you can turn on the above under
-overload by replacing line 8 with: 
        
+
      •  
         You can automatically turn on the above overload measure
+with Postfix 2.5 and later, or with earlier releases that contain
+the stress-adaptive behavior source code patch from the mirrors
+listed at http://www.postfix.org/download.html. Simply replace line
+above 8 with: 
        
 
 
          8      rbl_reply_maps = ${stress?hash:/etc/postfix/rbl_reply_maps}
 
        
 
-
         More information about automatic stress-adaptive behavior is
-at the end of this document. 
        
-
 
      
 
-
       Take desperate measures 
      
+
       More information about automatic stress-adaptive behavior is
+in section "Automatic stress-adaptive behavior".
+
      
 
-
       The following measures will still allow most legitimate
-clients to connect and send mail, but may affect some legitimate
-clients. 
      
+
       Temporary measures for older Postfix releases 
      
+
+
       See the next section, "Automatic stress-adaptive
+behavior", if you are running Postfix version 2.5 or later, or
+if you have applied the source code patch for stress-adaptive
+behavior from the mirrors listed at http://www.postfix.org/download.html.
+
      
+
+
       The following measures can be applied temporarily during overload.
+They still allow most legitimate clients to connect and send
+mail, but may affect some legitimate clients. 
      
 
 
        
 
@@ -312,16 +330,9 @@ such as a mailing list that contains a few no-longer-active user
 names that didn't bother to unsubscribe. No mail should be lost,
 as long as this measure is used only temporarily. 
        
 
-
      •  
         Disable remote SMTP client hostname lookups, so that all
-SMTP client hostnames become "unknown" (line 5 below). This feature
-was introduced with Postfix 2.3. Unfortunately, this measure is
-more problematic than the other ones proposed sofar.  First, this
-will result in loss of mail when you use hostname-based access rules
-that reject mail from "unknown" SMTP clients (examples:
-reject_unknown_client_hostname, reject_unknown_reverse_client_hostname).
-Second, this may result in loss of mail when you subject "unknown"
-SMTP clients to additional restrictions such as reject_unverified_sender.
-
        
+
      •  
         Use an smtpd_junk_command_limit of 1 instead of the default
+100. This prevents clients from keeping idle connections open by
+repeatedly sending NOOP or RSET commands. 
        
 
 
      
 
@@ -330,40 +341,60 @@ SMTP clients to additional restrictions such as main.cf:
 2      smtpd_timeout = 10
 3      smtpd_hard_error_limit = 1
-4      # Caution: line 5 may trigger REJECTs by hostname-based access rules 
-5      smtpd_peername_lookup = no
+4      smtpd_junk_command_limit = 1
    -

    Except with the last measure, no mail should be lost, as long +

    With these measures, no mail should be lost, as long as these measures are used only temporarily. The next section of this document introduces a way to automate this process.

    -

    Make Postfix behavior stress-adaptive

    +

    Automatic stress-adaptive behavior

    Postfix version 2.5 introduces automatic stress-adaptive behavior. -This is also available as an add-on patch for Postfix versions 2.4 -and 2.3 from the mirrors listed at http://www.postfix.org/download.html. -

    +This is also available as a source code patch for Postfix versions +2.4 and 2.3 from the mirrors listed at +http://www.postfix.org/download.html.

    -

    It works as follows. When a "public" network service runs into -an "all server ports are busy" condition, the master(8) daemon logs -a warning, restarts the service (without interrupting existing -network sessions), and runs the service with "-o stress=yes" on the -command line. Normally, it runs a stress-adaptive service with "-o -stress=" on the command line (i.e. with an empty parameter value). -Other services never have "-o stress" parameters on the command -line, including services that listen on a loopback interface only. +

    It works as follows. When a "public" network service such as +the SMTP server runs into an "all server ports are busy" condition, +the Postfix master(8) daemon logs a warning, restarts the service +(without interrupting existing network sessions), and runs the +service with "-o stress=yes" on the server process command line:

    -

    The stress pseudo-parameter value is the key to making main.cf -parameter settings stress adaptive:

    - 
    -1  /etc/postfix/main.cf:
-2      smtpd_timeout = ${stress?10}${stress:300}
-3      smtpd_hard_error_limit = ${stress?1}${stress:20}
+80821  ??  S      0:00.24 smtpd -n smtp -t inet -u -c -o stress=yes
+
    +
    + +

    Normally, the Postfix master(8) daemon runs such a service with +"-o stress=" on the command line (i.e. with an empty parameter +value):

    + +
    +
    +83326  ??  S      0:00.28 smtpd -n smtp -t inet -u -c -o stress=
+
    +
    + +

    Services that have local access only never have "-o stress" +parameters on the command line. This includes services internal to +Postfix such as the queue manager, and services that listen on a +loopback interface only, such as after-filter SMTP services.

    + +

    The "stress" parameter value is the key to making main.cf +parameter settings stress adaptive. The following settings are the +default with Postfix 2.6 and later. With earlier Postfix versions +that have stress-adaptive support, append the lines below to the +main.cf file and issue a "postfix reload" command:

    + +
    +
    +1 smtpd_timeout = ${stress?10}${stress:300}s
+2 smtpd_hard_error_limit = ${stress?1}${stress:20}
+3 smtpd_junk_command_limit = ${stress?1}${stress:100}
    @@ -371,11 +402,29 @@ parameter settings stress adaptive:

    @@ -463,6 +512,20 @@ services that accept remote connections.

    +

    Other measures to off-load zombies

    + +

    OpenBSD spamd +implements a daemon that handles all connections from "new" clients. +Only well-behaved mail clients are allowed to talk to the mail +server. Other clients are tarpitted, and will never get a chance +to affect mail server performance.

    + +

    At some point in the future, Postfix may come with a simple +front-end daemon that does basic greylisting and pipelining detection +to keep zombies and other ratware away from Postfix itself. This +would use the "pass" service type which has been available in +stable Postfix releases since Postfix 2.5.

    +

    Credits

    diff --git a/postfix/html/postmulti.1.html b/postfix/html/postmulti.1.html index 896106ea8..645238e24 100644 --- a/postfix/html/postmulti.1.html +++ b/postfix/html/postmulti.1.html @@ -179,8 +179,8 @@ POSTMULTI(1) POSTMULTI(1) New or existing instance name assignment -I name Assign the specified instance name to an existing - instance or to a newly created or imported - instance. Instance names other than "-" (which + instance, newly-created instance, or imported + instance. Instance names other than "-" (which makes the instance "nameless") must start with "postfix-". This restriction reduces the likeli- hood of name collisions with system files. diff --git a/postfix/makedefs b/postfix/makedefs index ee4643610..483f8953d 100644 --- a/postfix/makedefs +++ b/postfix/makedefs @@ -599,7 +599,7 @@ ${WARN='-Wall -Wno-comment -Wformat -Wimplicit -Wmissing-prototypes \ export SYSTYPE AR ARFL RANLIB SYSLIBS CC OPT DEBUG AWK OPTS # Snapshot only. -CCARGS="$CCARGS -DSNAPSHOT" +#CCARGS="$CCARGS -DSNAPSHOT" # Non-production: needs thorough testing, or major changes are still # needed before the code stabilizes. diff --git a/postfix/man/man1/postmulti.1 b/postfix/man/man1/postmulti.1 index 36439722f..9d7c8b399 100644 --- a/postfix/man/man1/postmulti.1 +++ b/postfix/man/man1/postmulti.1 @@ -176,8 +176,9 @@ primary Postfix instance. .SH "New or existing instance name assignment" .IP "\fB-I \fIname\fR" Assign the specified instance \fIname\fR to an existing -instance or to a newly created or imported instance. Instance -names other than "-" (which makes the instance "nameless") +instance, newly-created instance, or imported instance. +Instance +names other than "-" (which makes the instance "nameless") must start with "postfix-". This restriction reduces the likelihood of name collisions with system files. .IP "\fB-G \fIgroup\fR" diff --git a/postfix/proto/SMTPD_POLICY_README.html b/postfix/proto/SMTPD_POLICY_README.html index 549a9d6e3..4ceb78cc3 100644 --- a/postfix/proto/SMTPD_POLICY_README.html +++ b/postfix/proto/SMTPD_POLICY_README.html @@ -126,10 +126,10 @@ stress= an empty value ("name="), or sends a zero value ("name=0") in the case of a numerical attribute.

    -

  • The "recipient" attribute is available only in the - "RCPT TO" stage, and in the "DATA" and "END-OF-MESSAGE" stages - when Postfix accepted only one recipient for the current message. -

    +

  • The "recipient" attribute is available in the "RCPT + TO" stage. It is also available in the "DATA" and "END-OF-MESSAGE" + stages if Postfix accepted only one recipient for the current + message.

  • The "recipient_count" attribute (Postfix 2.3 and later) is non-zero only in the "DATA" and "END-OF-MESSAGE" stages. It diff --git a/postfix/proto/STRESS_README.html b/postfix/proto/STRESS_README.html index 6df8cb662..31488359f 100644 --- a/postfix/proto/STRESS_README.html +++ b/postfix/proto/STRESS_README.html @@ -21,13 +21,11 @@ Stress-Dependent Configuration

    Overview

    This document describes the symptoms of Postfix SMTP server -overload, and how to avoid the condition under normal conditions. -When the condition is caused by botnets or other malware, the -document suggests configuration settings that help to minimize the -impact on legitimate mail. Finally, the document introduces -stress-adaptive behavior, introduced with Postfix 2.5, and how it -can be used to automatically switch configuration settings under -overload.

    +overload. It presents permanent main.cf changes to avoid overload +during normal operation, and temporary main.cf changes to cope with +an unexpected burst of mail. This document makes specific suggestions +for Postfix 2.5 and later which support stress-adaptive behavior, +and for earlier Postfix versions that don't.

    Topics covered in this document:

    @@ -41,47 +39,52 @@ overload.

  • Disconnect suspicious SMTP clients -
  • Take desperate measures +
  • Temporary measures for older Postfix releases -
  • Make Postfix behavior stress-adaptive +
  • Automatic stress-adaptive behavior
  • Detecting support for stress-adaptive behavior
  • Forcing stress-adaptive behavior on or off +
  • Other measures to off-load zombies +
  • Credits

    Symptoms of Postfix SMTP server overload

    -

    Under normal conditions, Postfix responds immediately when a -remote SMTP client connects. The time needed to deliver mail should -be noticeable only with very large messages. Performance degrades -more dramatically when the number of remote SMTP clients exceeds -the number of Postfix SMTP server processes. When a client connects -while all server processes are busy, the client must wait until a -server process becomes available.

    +

    Under normal conditions, the Postfix SMTP server responds +immediately when an SMTP client connects to it; the time to deliver +mail is noticeable only with large messages. Performance degrades +dramatically when the number of SMTP clients exceeds the number of +Postfix SMTP server processes. When an SMTP client connects while +all Postfix SMTP server processes are busy, the client must wait +until a server process becomes available.

    -

    Overload may be caused by a legitimate mail (example: a DNS -registrar opens a new zone for registrations), by mistake (mail -explosion caused by a forwarding loop) or by illegitimate mail (worm -outbreak, botnet, or other malware activity). Symptoms of Postfix -SMTP mail server overload are:

    +

    SMTP server overload may be caused by a surge of legitimate +mail (example: a DNS registrar opens a new zone for registrations), +by mistake (mail explosion caused by a forwarding loop) or by malice +(worm outbreak, botnet, or other illegitimate activity).

    + +

    Symptoms of Postfix SMTP server overload are:

    Legitimate mail that doesn't get through during an episode of -overload is not necessarily lost. It should still arrive once the -situation returns to normal, as long as the overload condition is -temporary.

    +Postfix SMTP server overload is not necessarily lost. It should +still arrive once the situation returns to normal, as long as the +overload condition is temporary.

    Service more SMTP clients at the same time

    -

    To service more SMTP clients simultaneously, you need to increase -the number of SMTP server processes. This will improve the +

    One measure to avoid the "all server processes busy" condition +is to service more SMTP clients simultaneously. For this you need +to increase the number of Postfix SMTP server processes. This will +improve the responsiveness for remote SMTP clients, as long as the server machine has enough hardware and software resources to run the additional processes, and as long as the file system can keep up with the @@ -137,7 +142,8 @@ later, and an operating system that supports kernel-based event filters (BSD kqueue(2), Linux epoll(4), or Solaris /dev/poll).

    -

  • You can reduce the Postfix memory footprint by using cdb: +

  • More processes use more memory. You can reduce the Postfix +memory footprint by using cdb: lookup tables instead of Berkeley DB's hash: or btree: tables. 

    @@ -181,9 +187,9 @@ Issue a "postfix reload" command to make the change effective.  
    
 
 
     When increasing the number of SMTP server processes is not
 practical, you can improve Postfix server responsiveness by eliminating
-unnecessary work. When Postfix spends less time per SMTP session, the
-same number of SMTP server processes can service more clients in the
-same amount of time. 
    
+delays.  When Postfix spends less time per SMTP session, the same
+number of SMTP server processes can service more clients in a given
+amount of time. 
    
 
 
      
 
@@ -201,18 +207,18 @@ emergency patterns to block the latest worm explosion or backscatter
 mail.  See BACKSCATTER_README for examples of the latter.
 
 
    •  
       Group your header_checks and body_checks patterns to avoid
-unnecessary pattern matching operations.
+unnecessary pattern matching operations:
 
 
        1  /etc/postfix/header_checks:
  2      if /^Subject:/
  3      /^Subject: virus found in mail from you/ reject
- 4      /^Subject: ..../ ....
+ 4      /^Subject: ..other../ reject
  5      endif
  6  
  7      if /^Received:/
  8      /^Received: from (postfix\.org) / reject forged client name in received header: $1
- 9      /^Received: from .../ ....
+ 9      /^Received: from ..other../ reject ....
 10      endif
 
      
 
@@ -226,20 +232,22 @@ clients get a chance to talk to Postfix.  
      
 
 
        
 
-
      •  
         Use "521" reply codes (Postfix 2.6 and later) for
-botnet-related RBLs or for selected non-RBL restrictions. With
-Postfix 2.3-2.5 use "421" for a similar result. The Postfix SMTP
-server will disconnect immediately without waiting for the remote
-SMTP client to send a QUIT command. 
        
+
      •  
         Use "521" SMTP reply codes (Postfix 2.6 and later) or "421"
+(Postfix 2.3-2.5) to hang up on clients that that match botnet-related
+RBLs (see next bullet) or that match selected non-RBL restrictions
+such as SMTP access maps.  The Postfix SMTP server will reject mail
+and disconnect without waiting for the remote SMTP client to send
+a QUIT command.  
        
 
-
         You can set individual reject codes for RBLs, and for individual
-responses from a specific RBL. We'll use zen.spamhaus.org as an
-example; by the time you read this document, details may have
-changed.  Right now, their documents say that a response of 127.0.0.10
-or 127.0.0.11 indicates a dynamic client IP address, which means
-that the machine is probably running a bot of some kind.  To give
-a 521 response instead of the default 554 response, use something
-like: 
        
+
      •  
         To hang up connections from blacklisted zombies, you can
+set specific Postfix SMTP server reject codes for specific RBLs,
+and for individual responses from specific RBLs. We'll use
+zen.spamhaus.org as an example; by the time you read this document,
+details may have changed.  Right now, their documents say that a
+response of 127.0.0.10 or 127.0.0.11 indicates a dynamic client IP
+address, which means that the machine is probably running a bot of
+some kind.  To give a 521 response instead of the default 554
+response, use something like: 
        
 
 
          1  /etc/postfix/main.cf:
@@ -252,45 +260,55 @@ like: 
        
  8      rbl_reply_maps = hash:/etc/postfix/rbl_reply_maps
  9  
 10  /etc/postfix/rbl_reply_maps:
-11      zen.spamhaus.org=127.0.0.10 521 4.7.1 Service unavailable;
-12       $rbl_class [$rbl_what] blocked using
-13       $rbl_domain${rbl_reason?; $rbl_reason}
-14  
-15      zen.spamhaus.org=127.0.0.11 521 4.7.1 Service unavailable;
-16       $rbl_class [$rbl_what] blocked using
-17       $rbl_domain${rbl_reason?; $rbl_reason}
+11      # With Postfix 2.3-2.5 use "421" to hang up connections.
+12      zen.spamhaus.org=127.0.0.10 521 4.7.1 Service unavailable;
+13       $rbl_class [$rbl_what] blocked using
+14       $rbl_domain${rbl_reason?; $rbl_reason}
+15  
+16      zen.spamhaus.org=127.0.0.11 521 4.7.1 Service unavailable;
+17       $rbl_class [$rbl_what] blocked using
+18       $rbl_domain${rbl_reason?; $rbl_reason}
 
        
 
-
         Although the above shows three RBL lookups (lines 4-6), Postfix
-will still only do a single DNS query, so the performance difference
-is negligible. 
        
+
         Although the above example shows three RBL lookups (lines 4-6),
+Postfix will only do a single DNS query, so it does not affect the
+performance. 
        
 
-
         With Postfix 2.3-2.5, use 421 (reply code 521 will not cause
-Postfix to disconnect). The down-side of sending 421 is that
-it works only for zombies and other malware. If the client is running
-a real MTA, then it may connect again several times until the mail
-expires in its queue. When this is a problem, stick with the default
-554 reply, and use "smtpd_hard_error_limit = 1" as described below.
-
        
+
      •  
         With Postfix 2.3-2.5, use reply code 421 (521 will not
+cause Postfix to disconnect). The down-side of replying with 421
+is that it works only for zombies and other malware. If the client
+is running a real MTA, then it may connect again several times until
+the mail expires in its queue. When this is a problem, stick with
+the default 554 reply, and use "smtpd_hard_error_limit = 1" as
+described below.  
        
 
-
         With Postfix 2.5, or with earlier releases that contain the
-stress-adaptive behavior patch, you can turn on the above under
-overload by replacing line 8 with: 
        
+
      •  
         You can automatically turn on the above overload measure
+with Postfix 2.5 and later, or with earlier releases that contain
+the stress-adaptive behavior source code patch from the mirrors
+listed at http://www.postfix.org/download.html. Simply replace line
+above 8 with: 
        
 
 
          8      rbl_reply_maps = ${stress?hash:/etc/postfix/rbl_reply_maps}
 
        
 
-
         More information about automatic stress-adaptive behavior is
-at the end of this document. 
        
-
 
      
 
-
       Take desperate measures 
      
+
       More information about automatic stress-adaptive behavior is
+in section "Automatic stress-adaptive behavior".
+
      
 
-
       The following measures will still allow most legitimate
-clients to connect and send mail, but may affect some legitimate
-clients. 
      
+
       Temporary measures for older Postfix releases 
      
+
+
       See the next section, "Automatic stress-adaptive
+behavior", if you are running Postfix version 2.5 or later, or
+if you have applied the source code patch for stress-adaptive
+behavior from the mirrors listed at http://www.postfix.org/download.html.
+
      
+
+
       The following measures can be applied temporarily during overload.
+They still allow most legitimate clients to connect and send
+mail, but may affect some legitimate clients. 
      
 
 
        
 
@@ -312,16 +330,9 @@ such as a mailing list that contains a few no-longer-active user
 names that didn't bother to unsubscribe. No mail should be lost,
 as long as this measure is used only temporarily. 
        
 
-
      •  
         Disable remote SMTP client hostname lookups, so that all
-SMTP client hostnames become "unknown" (line 5 below). This feature
-was introduced with Postfix 2.3. Unfortunately, this measure is
-more problematic than the other ones proposed sofar.  First, this
-will result in loss of mail when you use hostname-based access rules
-that reject mail from "unknown" SMTP clients (examples:
-reject_unknown_client_hostname, reject_unknown_reverse_client_hostname).
-Second, this may result in loss of mail when you subject "unknown"
-SMTP clients to additional restrictions such as reject_unverified_sender.
-
        
+
      •  
         Use an smtpd_junk_command_limit of 1 instead of the default
+100. This prevents clients from keeping idle connections open by
+repeatedly sending NOOP or RSET commands. 
        
 
 
      
 
@@ -330,40 +341,60 @@ SMTP clients to additional restrictions such as reject_unverified_sender.
 1  /etc/postfix/main.cf:
 2      smtpd_timeout = 10
 3      smtpd_hard_error_limit = 1
-4      # Caution: line 5 may trigger REJECTs by hostname-based access rules 
-5      smtpd_peername_lookup = no
+4      smtpd_junk_command_limit = 1
    -

    Except with the last measure, no mail should be lost, as long +

    With these measures, no mail should be lost, as long as these measures are used only temporarily. The next section of this document introduces a way to automate this process.

    -

    Make Postfix behavior stress-adaptive

    +

    Automatic stress-adaptive behavior

    Postfix version 2.5 introduces automatic stress-adaptive behavior. -This is also available as an add-on patch for Postfix versions 2.4 -and 2.3 from the mirrors listed at http://www.postfix.org/download.html. -

    +This is also available as a source code patch for Postfix versions +2.4 and 2.3 from the mirrors listed at +http://www.postfix.org/download.html.

    -

    It works as follows. When a "public" network service runs into -an "all server ports are busy" condition, the master(8) daemon logs -a warning, restarts the service (without interrupting existing -network sessions), and runs the service with "-o stress=yes" on the -command line. Normally, it runs a stress-adaptive service with "-o -stress=" on the command line (i.e. with an empty parameter value). -Other services never have "-o stress" parameters on the command -line, including services that listen on a loopback interface only. +

    It works as follows. When a "public" network service such as +the SMTP server runs into an "all server ports are busy" condition, +the Postfix master(8) daemon logs a warning, restarts the service +(without interrupting existing network sessions), and runs the +service with "-o stress=yes" on the server process command line:

    -

    The stress pseudo-parameter value is the key to making main.cf -parameter settings stress adaptive:

    - 
    -1  /etc/postfix/main.cf:
-2      smtpd_timeout = ${stress?10}${stress:300}
-3      smtpd_hard_error_limit = ${stress?1}${stress:20}
+80821  ??  S      0:00.24 smtpd -n smtp -t inet -u -c -o stress=yes
+
    +
    + +

    Normally, the Postfix master(8) daemon runs such a service with +"-o stress=" on the command line (i.e. with an empty parameter +value):

    + +
    +
    +83326  ??  S      0:00.28 smtpd -n smtp -t inet -u -c -o stress=
+
    +
    + +

    Services that have local access only never have "-o stress" +parameters on the command line. This includes services internal to +Postfix such as the queue manager, and services that listen on a +loopback interface only, such as after-filter SMTP services.

    + +

    The "stress" parameter value is the key to making main.cf +parameter settings stress adaptive. The following settings are the +default with Postfix 2.6 and later. With earlier Postfix versions +that have stress-adaptive support, append the lines below to the +main.cf file and issue a "postfix reload" command:

    + +
    +
    +1 smtpd_timeout = ${stress?10}${stress:300}s
+2 smtpd_hard_error_limit = ${stress?1}${stress:20}
+3 smtpd_junk_command_limit = ${stress?1}${stress:100}
    @@ -371,11 +402,29 @@ parameter settings stress adaptive:

    @@ -463,6 +512,20 @@ services that accept remote connections.

    +

    Other measures to off-load zombies

    + +

    OpenBSD spamd +implements a daemon that handles all connections from "new" clients. +Only well-behaved mail clients are allowed to talk to the mail +server. Other clients are tarpitted, and will never get a chance +to affect mail server performance.

    + +

    At some point in the future, Postfix may come with a simple +front-end daemon that does basic greylisting and pipelining detection +to keep zombies and other ratware away from Postfix itself. This +would use the "pass" service type which has been available in +stable Postfix releases since Postfix 2.5.

    +

    Credits