This is the Postfix 3.11 stable release.

The stable Postfix release is called postfix-3.11.x where 3=major
release number, 11=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-3.12-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 3.9 or earlier, please read RELEASE_NOTES-3.10
before proceeding.

Dual license
------------

As of Postfix 3.2.5 this software is distributed with a dual license:
in addition to the historical IBM Public License (IPL) 1.0, it is
now also distributed with the more recent Eclipse Public License
(EPL) 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 - database
------------------------

[Incompat 20260220] The alias_maps and alias_database parameter
default values have changed from hash:/path/to/aliases (or
dbm:/path/to/aliases) to $default_database_type:/path/to/aliases.
This simplifies the migration away from Berkeley DB.

[Infrastructure 20260219] Support to migrate a Postfix configuration
that uses Berkeley DB hash: or btree: tables, to a configuration
that uses lmdb: or a combination of cdb: and lmdb:. This is needed
for (Linux) OS distributions that have removed Berkeley DB support.
See NON_BERKELEYDB_README for manual and automatic migration support.

Postfix already supports CDB and LMDB for more than 10 years.  It
may be a good idea to do the migration before you need to upgrade
to an OS distribution that no longer supports Berkeley DB.

[Infrastructure 20251226] Tooling to help with the migration away
from Berkeley DB. 

The new parameter default_cache_db_type controls the default database
type for address_verify_map, postscreen_cache_map, and
smtp_sasl_auth_cache_name, previously hard-coded as 'btree'.

[Feature 20250321] Safety: the SQLite client now logs a warning
when a query uses double quotes instead of the Postfix-recommended
single quotes. Only the recommended form is protected against SQL
injection.

[Feature 20250509] Support to run all memcache lookup keys through
an OpenSSL digest function. This prevents a database access error
when lookup keys may exceed the memcache server's key length limit
(usually, 250 bytes).

[Feature 20250624] Support for a new "debug:" pseudo lookup table.
Specify debug:maptype:mapname to encapsulate a maptype:mapname
lookup table and log all access. This builds on existing but unused
code to log table access. Contributed by Richard Hansen.

[Infrastructure 20250626] Overhauled in-memory lookup table life-cycle
management; overhauled sharing/isolation for proxied lookup tables.

Major changes - deprecation
---------------------------

[Feature 20250609] smtp_tls_enforce_peername and lmtp_tls_enforce_peername
are now officially deprecated. Postfix will log a warning until the
features are deleted. See DEPRECATION_README for a summary of
deprecated and deleted features.

[Feature 20251027] This adds 12 more deprecation warnings for
parameters that have been renamed in the past, and that still provide
a backwards-compatible default value for their replacement. The
parameters deprecated by this change are: authorized_verp_clients,
fallback_relay, lmtp_per_record_deadline, postscreen_blacklist_action,
postscreen_dnsbl_ttl, postscreen_dnsbl_whitelist_threshold,
postscreen_whitelist_interfaces, smtpd_client_connection_limit_exceptions,
smtp_per_record_deadline, tlsproxy_client_level, tlsproxy_client_policy,
virtual_maps.

[Feature 20251028] Deprecate the smtp_cname_overrides_servername
and lmtp_cname_overrides_servername parameters, and delete documentation
that has been obsolete since Postfix 2.11.

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

[Feature 20250910] TLS feature policy status summary in delivery
status logging. This shows the desired and actual TLS security level
enforcement status and, if a message requests REQUIRETLS, the
REQUIRETLS policy enforcement status. For a list of examples see
https://www.postfix.org/postconf.5.html#smtp_log_tls_feature_status

[Feature 20251216] After a delivery failure, the bounce daemon
logged "<old-queue-id>: sender non-delivery notification: <new-queue-id>"
only if the notification was queued successfully. The bounce daemon
now always logs this, making Postfix behavior easier to understand.

Visible changes for logfile analyzers:

- The bounce daemon now logs "<old-queue-id>: sender non-delivery
notification: <new-queue-id>" BEFORE the cleanup daemon logs activity
with "<new-queue-id>". Previously, the bounce daemon logged the
old<=>new queue ID connection later, which made logfile analysis
more difficult.

- The bounce daemon now logs a logfile record "<old-queue-id>:
sender notification failed to <address>: <reason>" when the
notification was not queued. In some cases it will log "<old-queue-id>:
sender notification failed to <address>" (without the reason). In
those cases the failure reason was already logged by lower-level
code, but without the queue ID.

Major changes - management tool integration
-------------------------------------------

[Feature 20251124] Basic JSON output support with "postconf
-j|-jM|-jF|-jP", "postalias -jq|-js", "postmap -jq|-js", and
"postmulti -jl". No support is planned for JSON input support.

Major changes - milter support
------------------------------

[Feature 20251208] Improved Milter error handling for messages that
arrive over a long-lived SMTP connection, by changing the default
milter_default_action from "tempfail" to the new "shutdown" action
(i.e. disconnect the remote SMTP client).

This avoids a worst-case scenario where after a single Milter error,
Postfix would tempfail all messages that the client sends over a
long-lived connection, even if the Milter error was only temporary.

Major changes - mime support
----------------------------

[Feature 20251104] New non_empty_end_of_header_action parameter
with the cleanup(8) server action when a primary message header is
terminated with a non-empty line:

1) fix_quietly: Insert an empty line before the offending text (the
backwards-compatible default),

2) add_header: Insert a MIME-Error: header before inserting an empty
line, or

3) reject: Log a "mime-error" and reject the message.

Note that the 'empty line' separator is not used for DKIM signature
checks. Therefore, adding a missing separator does not break DKIM.

Major changes - mta-sts
-----------------------

[Feature 20250906] Workaround for an interface mis-match between
the Postfix SMTP client and MTA-STS policy plugins. This introduces
a new parameter "smtp_tls_enforce_sts_mx_patterns" (default: "yes").
The MTA-STS plugin configuration needs to enable TLSRPT support,
so that it forwards STS policy attributes to Postfix. This works
even if Postfix TLSRPT support is disabled at build time or at
runtime.

With the above two configurations, the Postfix SMTP client will
connect to an MX host only if its name matches any STS policy MX
host pattern, and will match a server certificate against the MX
hostname. Otherwise, the old behavior stays in effect: connect to
any MX host listed in DNS, and match a server certificate against
any STS policy MX host pattern.

This code was published first in Postfix 3.11, and later back-ported
to Postfix 3.10.5.

Major changes - portability
---------------------------

[Feature 20241201] Support for the C23 built-in bool type. Older
Postfix releases have been updated with a makedefs script that
disables C23 built-in bool support.

Major changes - postqueue
-------------------------

[Feature 20251218] the postqueue (and mailq) command now also lists
recipients in bounce logfiles (in JSON output, this uses a new
object member 'bounce_reason' instead of the existing 'delay_reason').
Such recipients have already been deleted from the message queue
file, but they are still pending the creation of a non-delivery
status notification message that will be returned to the sender.

Major changes - relocated_maps
------------------------------

[Feature 20250608] Specify "relocated_prefix_enable = no" to disable
the hard-coded prefix "5.1.6 User has moved to " that is by default
prepended to all relocated_maps lookup results. This setting requires
that the table contains responses with both custom enhanced status
code (X.Y.Z) and text. For details, see "man 5 relocated" or
https://www.postfix.org/relocated.5.html .

Major changes - requiretls
--------------------------

[Feature 20241111] Support for the REQUIRETLS verb in SMTP. This,
and everything that was added later through 2025, is described in
REQUIRETLS_README.

[Feature 20250120] After a certificate check fails, or a remote
SMTP server does not announce REQUIRETLS support, the Postfix SMTP
client will override the RFC 8689 5.x.x.  status and treat it as a
soft error, until there are no more alternate MX servers to try.

[Feature 20250827] New parameter requiretls_redact_dsn (default:
yes) to redact bounce messages as described in RFC 8689 section 5,
so that they don't need REQUIRETLS support on every hop in the
return path.

[Feature 20250827] smtp_requiretls_policy and lmtp_requiretls_policy
for responsible REQUIRETLS policy enforcement. REQUIRETLS must be
enforced with care, because at this time most domains do not publish
DANE or MTA-STS policies, and most MTAs and content filters do not
support REQUIRETLS.

[Feature 20250916] support for a "Require-TLS-ESMTP: yes" header
to propagate an ESMTP REQUIRETLS request through a FILTER_README
or SMTPD_PROXY_README style content filter. This header is detected
or added by the cleanup daemon and by the before-proxy-filter Postfix
SMTP server. This feature is enabled by default with
"requiretls_esmtp_header = yes". The Require-TLS-ESMTP header will
be visible to local and remote recipients. This feature can safely
be disabled when a configuration does not use REQUIRETLS, or does
not use FILTER_README or SMTPD_PROXY_README style content filters.

Major changes - smtp server
---------------------------

[Feature 20250801] smtpd_reject_filter_maps support to selectively
replace a reject response from the Postfix SMTP server, or from a
program that replies through the Postfix SMTP server.

Major changes - smtputf8
------------------------

[Feature 20250122] New Postfix sendmail command option "-O smtputf8"
to request that deliveries over SMTP use the SMTPUTF8 extension.
This reuses logic that was introduced for REQUIRETLS.

[Feature 20250824] When a message needs to be delivered with SMTPUTF8,
but a remote server does not support it, the Postfix SMTP client
may now try alternate servers instead of returning the message
immediately. This reuses code that was implemented for REQUIRETLS.

Major changes - tls support
---------------------------

[Feature 20250623] This changes the Postfix SMTP client
smtp_tls_security_level default value to "may" if Postfix was built
with TLS support, and the compatibility_level is 3.11 or higher.

There is no change to the default lmtp_tls_security_level value.
It remains empty, because there is no default TLS security level
that makes sense for connections over UNIX-domain and loopback TCP
and non-loopback TCP sockets.

There also is no equivalent change for Postfix SMTP server TLS
security levels, because changing smtpd_tls_security_level is not
sufficient. Server-side TLS requires that at least one private key
and corresponding public-key certificate chain are configured.

[Feature 20251029] Debugging: depending on OpenSSL build options,
"posttls-finger -L ssl-debug" will decode TLS handshake messages.

[Feature 20251102] Post-quantum cryptography support: with OpenSSL
3.5 and later, change the tls_eecdh_auto_curves default value to
avoid problems with network infrastructure that mis-handles TLS
hello messages larger than one (Ethernet) TCP segment. This problem
is more generally known as "protocol ossification".

Major changes - tlsrpt
----------------------

[Incompat 20250601] the default smtp_tlsrpt_skip_reused_handshakes
setting was changed from "yes" to "no". The new default is enabled
with compatibility level >= 3.11.

