This is the Postfix 3.5 (stable) release.

The stable Postfix release is called postfix-3.5.x where 3=major
release number, 5=minor release number, x=patchlevel.  The stable
release never changes except for patches that address bugs or
emergencies. Patches change the patchlevel and the release date.

New features are developed in snapshot releases. These are called
postfix-3.6-yyyymmdd where yyyymmdd is the release date (yyyy=year,
mm=month, dd=day).  Patches are never issued for snapshot releases;
instead, a new snapshot is released.

The mail_release_date configuration parameter (format: yyyymmdd)
specifies the release date of a stable release or snapshot release.

If you upgrade from Postfix 3.3 or earlier, read RELEASE_NOTES-3.4
before proceeding.

License change
---------------

This software is distributed with a dual license: in addition to the
historical IBM Public License 1.0, it is now also distributed with the
more recent Eclipse Public License 2.0. Recipients can choose to take
the software under the license of their choice. Those who are more
comfortable with the IPL can continue with that license.

Major changes - multiple relayhost in SMTP
------------------------------------------

[Feature 20200111] the Postfix SMTP and LMTP client support a list
of nexthop destinations separated by comma or whitespace. These
destinations will be tried in the specified order.

The list form can be specified in relayhost, transport_maps,
default_transport, and sender_dependent_default_transport_maps.

Examples:
/etc/postfix/main.cf:
    relayhost = foo.example, bar.example
    default_transport = smtp:foo.example, bar.example.

NOTE: this is an SMTP and LMTP client feature. It does not work for
other Postfix delivery agents.

Major changes - certificate access
----------------------------------

[Feature 20190517] Search order support for check_ccert_access.
Search order support for other tables is in design (canonical_maps,
virtual_alias_maps, transport_maps, etc.).

The following check_ccert_access setting uses the built-in search
order: it first looks up the client certificate fingerprint, then
the client certificate public-key fingerprint, and it stops when a
decision is made.

/etc/postfix/main.cf:
    smtpd_mumble_restrictions =
        ...
        check_ccert_access hash:/etc/postfix/ccert-access
        ...

The following setting, with explicit search order, produces the
exact same result:

/etc/postfix/main.cf:
    smtpd_mumble_restrictions =
        ...
        check_ccert_access {
            hash:/etc/postfix/ccert-access {
                search_order = cert_fingerprint, pubkey_fingerprint } }
        ...

Support is planned for other certificate features.

Major changes - dovecot usability
---------------------------------

[Feature 20190615] The SMTP+LMTP delivery agent can now prepend
Delivered-To, X-Original-To and Return-Path headers, just like the
pipe(8) and local(8) delivery agents. 

This uses the "flags=DORX" command-line flags in master.cf. See the
smtp(8) manpage for details.

This obsoletes the "lmtp_assume_final = yes" setting, and replaces
it with "flags=...X...", for consistency with the pipe(8) delivery
agent.

Major changes - forced expiration
---------------------------------

[Feature 20200202] Support to force-expire email messages. This
introduces new postsuper(1) command-line options to request expiration,
and additional information in mailq(1) or postqueue(1) output.

The forced-to-expire status is stored in a queue file attribute.
An expired message is returned to the sender when the queue manager
attempts to deliver that message (note that Postfix will never
deliver messages in the hold queue).

The postsuper(1) -e and -f options both set the forced-to-expire
queue file attribute. The difference is that -f will also release
a message if it is in the hold queue. With -e, such a message would
not be returned to the sender until it is released with -f or -H.

In the mailq(1) or postqueue(1) -p output, a forced-to-expire message
is indicated with # after the queue file name. In postqueue(1) JSON
output, there is a new per-message field "forced_expire" (with value
true or false) that shows the forced-to-expire status.

Major changes - haproxy2 protocol
---------------------------------

[Feature 20200112] Support for the haproxy v2 protocol. The Postfix
implementation supports TCP over IPv4 and IPv6, as well as non-proxied
connections; the latter are typically used for heartbeat tests.

The haproxy v2 protocol introduces no additional Postfix configuration.
The Postfix smtpd(8) and postscreen(8) daemons accept both v1 and
v2 protocol versions.

Major changes - logging
-----------------------

[Incompat 20191109] Postfix daemon processes now log the from= and
to= addresses in external (quoted) form in non-debug logging (info,
warning, etc.).  This means that when an address localpart contains
spaces or other special characters, the localpart will be quoted,
for example:

    from=<"name with spaces"@example.com>

Older Postfix versions would log the internal (unquoted) form:

    from=<name with spaces@example.com>

The external and internal forms are identical for the vast majority
of email addresses that contain no spaces or other special characters
in the localpart.

Specify "info_log_address_format = internal" for backwards
compatibility.

The logging in external form is consistent with the address form
that Postfix 3.2 and later prefer for table lookups. It is therefore
the more useful form for non-debug logging.

Major changes - IP address normalization
----------------------------------------

[Incompat 20190427] Postfix now normalizes IP addresses received
with XCLIENT, XFORWARD, or with the HaProxy protocol, for consistency
with direct connections to Postfix. This may change the appearance
of logging, and the way that check_client_access will match subnets
of an IPv6 address.
