This is the Postfix 3.9 stable release.

The stable Postfix release is called postfix-3.9.x where 3=major
release number, 9=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-3.10-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 3.7 or earlier, please read RELEASE_NOTES-3.8
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.

Topics in this document
-----------------------
- changes that are less visible
- database support
- envid support
- feature deprecation
- mime conversion
- protocol compliance
- security
- tls support

Changes that are less visible
-----------------------------

The documentation has been updated to address many questions
that were asked on the postfix-users mailing list.

More unit tests to make Postfix future-proof. Wietse is now looking
into migrating unit tests to Google test, because other people are
familiar with that framework, than with a Postfix-specific one.

Major changes - database support
--------------------------------

[Feature 20240208] MongoDB client support, contributed by Hamid
Maadani, based on earlier code by Stephan Ferraro. For build and
usage instructions see MONGODB_README and mongodb_table(5).

[Feature 20240129] In the mysql: and pgsql: clients, the hard-coded
idle and retry timer settings are now configurable. Details are in
the updated mysql_table(5) and pgsql_table(5) manpages.

[Incompat 20230903] The MySQL client no longer supports MySQL
versions < 4.0. MySQL version 4.0 was released in 2003.

[Incompat 20230419] The MySQL client default characterset is now
configurable with the "charset" configuration file attribute. The
default is "utf8mb4", consistent with the MySQL 8.0 built-in default,
but different from earlier MySQL versions where the built-in default
was "latin1".

Major changes - envid support
-----------------------------

[Feature 20230901] The local(8) delivery agent exports an ENVID
environment variable with the RFC 3461 envelope ID if available.

The pipe(8) delivery agent supports an ${envid} command-line attribute
that expands to the RFC 3461 envelope ID if available.

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

[Incompat 20240218] The new document DEPRECATION_README covers
features that have been removed and that will be removed in the
future, with suggestions how to migrate.

The Postfix SMTP server logs a warning when "permit_mx_backup" is
used (support for restriction "permit_mx_backup" will be removed
from Postfix; instead, use "relay_domains"). File: smtpd/smtpd_check.c.

The postconf command logs a warning when the following parameters
are specified in main.cf or master.cf: xxx_use_tls, xxx_enforce_tls
(use the corresponding xxx_security_level setting instead);
xxx_per_site (use the corresponding xxx_policy_maps setting instead);
disable_dns_lookups (use smtp_dns_support_level instead);
smtpd_tls_dh1024_param_file, smtpd_tls_eecdh_grade (do not specify,
leave at default). These warning are silenced with the "postconf
-q".

[Incompat 20240218] The Postfix SMTP server now logs that
permit_naked_ip_address, reject_maps_rbl, and check_relay_domains
have been removed and suggests a replacement. These features have
been logging deprecation warnings since 2005 or earlier, and were
removed from Postfix documentation in 2004.

Major changes - mime conversion
-------------------------------

[Feature 20230901] New parameter force_mime_input_conversion (default:
no) to convert body content that claims to be 8-bit into quoted-printable,
before header_checks, body_checks, Milters, and before after-queue
content filters. This feature does not affect messages that are
sent into smtpd_proxy_filter.

The typical use case is an MTA that applies this conversion before
signing outbound messages, so that the signatures will remain valid
when a message is later handled by an MTA that does not announce
8BITMIME support, or when a message line exceeds the SMTP length
limit.

Major changes - protocol compliance
-----------------------------------

[Incompat 20240206] In message headers, Postfix now formats numerical
days as two-digit days, i.e. days 1-9 have a leading zero instead
of a leading space.  This change was made because the RFC 5322 date
and time specification recommends (i.e. SHOULD) that a single space
be used in each place that FWS appears. This change avoids a breaking
change in the date string length.

Major changes - security
------------------------

[Incompat 20240226] The Postfix DNS client now limits the total
size of DNS lookup results to 100 records; it drops the excess
records, and logs a warning. This limit is 20x larger than the
number of server addresses that the Postfix SMTP client is willing
to consider when delivering mail, and is far below the number of
records that could cause a tail recursion crash in dns_rr_append()
as reported by Toshifumi Sakaguchi.

This change introduces a similar limit on the number of DNS requests
that a check_*_*_access restriction can make.

[Incompat 20240110] With "cleanup_replace_stray_cr_lf = yes" (the
default), the cleanup daemon replaces each stray <CR> or <LF>
character in message content with a space character. The replacement
happens before any other content management (header/body_checks,
Milters, etc).

This prevents outbound SMTP smuggling, where an attacker uses Postfix
to send email containing a non-standard End-of-DATA sequence, to
exploit inbound SMTP smuggling at a vulnerable remote SMTP server.

This also improves the remote evaluation of Postfix-added DKIM and
other signatures, as the evaluation result will not depend on how
a remote email server handles stray <CR> or <LF> characters.

This feature applies to all email that Postfix locally or remotely
sends out. It is not allowlisted based on client identity.

[Feature 20240118] This updates Postfix fixes for inbound SMTP smuggling
attacks. For background, see https://www.postfix.org/smtp-smuggling.html

This will be back ported to Postfix 3.8.5, 3.7.10, 3.6.14, and 3.5.24.

- Better compatibility: the recommended setting "smtpd_forbid_bare_newline
  = normalize" requires the standard End-of-DATA sequence
  <CR><LF>.<CR><LF>, but allows bare newlines from SMTP clients,
  maintaining more compatibility with existing infrastructure.

- Improved logging for rejected input (it now includes queue ID,
  helo, mail, and rcpt, if available).

- The setting "smtpd_forbid_bare_newline = reject" requires
  that input lines end in <CR><LF>, requires the standard End-of-DATA
  sequence <CR><LF>.<CR><LF>, and rejects a command or message that
  contains a bare newline. To disconnect the client, specify
  "smtpd_forbid_bare_newline_reject_code = 521".

- The Postfix SMTP server no longer strips extra <CR> as in
  <CR><LF>.<CR><CR><LF>, to silence false alarms from test tools
  that send attack sequences that real mail servers cannot send.
  Details at https://www.postfix.org/false-smuggling-claims.html

- The old setting "yes" has become an alias for "normalize".

- The old setting "no" has not changed, and allows SMTP smuggling.

The recommended settings are now:

    # Require the standard End-of-DATA sequence <CR><LF>.<CR><LF>.
    # Otherwise, allow bare <LF> and process it as if the client sent
    # <CR><LF>.
    #
    # This maintains compatibility with many legitimate SMTP client
    # applications that send a mix of standard and non-standard line
    # endings, but will fail to receive email from client implementations
    # that do not terminate DATA content with the standard End-of-DATA
    # sequence <CR><LF>.<CR><LF>.
    #
    # Such clients can be allowlisted with smtpd_forbid_bare_newline_exclusions.
    # The example below allowlists SMTP clients in trusted networks.
    #
    smtpd_forbid_bare_newline = normalize
    smtpd_forbid_bare_newline_exclusions = $mynetworks

Alternative settings:

    # Reject input lines that contain <LF> and log a "bare <LF> received"
    # error. Require that input lines end in <CR><LF>, and require the
    # standard End-of-DATA sequence <CR><LF>.<CR><LF>.
    #
    # This will reject email from SMTP clients that send any non-standard
    # line endings such as web applications, netcat, or load balancer
    # health checks.
    #
    # This will also reject email from services that use BDAT to send
    # MIME text containing a bare newline (RFC 3030 Section 3 requires
    # canonical MIME format for text message types, defined in RFC 2045
    # Sections 2.7 and 2.8).
    #
    # Such clients can be allowlisted with smtpd_forbid_bare_newline_exclusions.
    # The example below allowlists SMTP clients in trusted networks.
    #
    smtpd_forbid_bare_newline = reject
    smtpd_forbid_bare_newline_exclusions = $mynetworks
    #
    # Alternatively, in the case of BDAT violations, BDAT can be selectively
    # disabled with smtpd_discard_ehlo_keyword_address_maps, or globally
    # disabled with smtpd_discard_ehlo_keywords.
    #
    # smtpd_discard_ehlo_keyword_address_maps = cidr:/path/to/file
    # /path/to/file:
    #     10.0.0.0/24 chunking, silent-discard
    # smtpd_discard_ehlo_keywords = chunking, silent-discard

[Incompat 20230603] the Postfix SMTP server by default disconnects
remote SMTP clients that violate RFC 2920 (or 5321) command pipelining
constraints. The server replies with "554 5.5.0 Error: SMTP protocol
synchronization" and logs the unexpected remote SMTP client input.
Specify "smtpd_reject_unauth_pipelining = no" to disable.

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

[Feature 20230807] Optional Postfix TLS support to request an RFC7250
raw public key instead of an X.509 public-key certificate. The
configuration settings for raw key public support will be ignored
when there is no raw public key support in the local TLS implementation
(i.e.  Postfix with OpenSSL versions before 3.2).

- With "smtpd_tls_enable_rpk = yes", the Postfix SMTP server will
  request that a remote SMTP client sends an RFC7250 raw public key
  instead of an X.509 certificate when asking for or requiring TLS
  client authentication. The Postfix SMTP server will still accept
  a client public-key certificate instead of a public key.

- With "smtp_tls_enable_rpk = yes" (or "enable_rpk = yes" in an
  smtp policy table) at the security levels "may", "encrypt" or
  "fingerprint", the Postfix SMTP client will request that a remote
  SMTP server sends an RFC7250 raw public key instead of an X.509
  certificate. The Postfix SMTP client will still accept a server
  public key certificate instead of a public key.

- At the "secure" and "verify" security level, the Postfix SMTP
  client will ignore smtp_tls_enable_rpk or enable_rpk settings,
  because these levels require a server certificate.

- At the "dane" and "dane-only" security levels, the Postfix SMTP
  client will ignore smtp_tls_enable_rpk or enable_rpk settings,
  and will request that a remote SMTP server sends an RFC7250 raw
  public key instead of an X.509 certificate when all valid TLSA
  records specify only server public keys (no certificates). The
  Postfix SMTP client will still accept a server public key
  certificate.

- The Postfix SMTP client and server always send a raw public key
  instead of a certificate, if solicited by the remote SMTP peer
  and the local TLS implementation supports raw public keys.

- If a remote SMTP client sends a server name indication with an
  SNI TLS extension, and tls_server_sni_maps is configured, the
  Postfix SMTP server will extract a raw public key from the indicated
  certificate.

Caution: enabling Postfix raw key support will break authentication
based on certificate fingerprints in check_ccert_access or
smtp_tls_policy_maps, when a remote peer's TLS implementation starts
to send a raw public key instead of a certificate. The solution is
to always use public key fingerprint patterns; these will match not
only a "raw" public key, but also the public key in a certificate.

To detect such problems before they happen, the Postfix SMTP server
will log a warning when it requests an RFC7250 raw public key instead
of an X.509 certificate, the remote peer sends a certificate instead
of a public key, and check_ccert_access has a matching fingerprint
for the certificate but not for the public key in that certificate.
There is no corresponding warning from the Postfix SMTP client.

For instructions to generate public-key fingerprints, see the
postconf(5) man pages for smtp_tls_enable_rpk and smtpd_tls_enable_rpk.

[Feature 20230522] Preliminary support for OpenSSL configuration
files, primarily OpenSSL 1.1.1b and later. This introduces two new
parameters "tls_config_file" and "tls_config_name", which can be
used to limit collateral damage from OS distributions that crank
up security to 11, increasing the number of plaintext email deliveries.
Details are in the postconf(5) manpage under "tls_config_file" and
"tls_config_name".
