This is the Postfix 3.7 (experimental) release.

The stable Postfix release is called postfix-3.6.x where 3=major
release number, 6=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-3.7-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 3.5 or earlier, read RELEASE_NOTES-3.6
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 with snapshot 20211127
====================================

Support for the pcre2 library (the legacy pcre library is no longer
maintained). The Postfix build procedure automatically detects if
the pcre2 library is installed, and if it is unavailable, the Postfix
build procedure will detect if the legacy pcre library is installed.
See PCRE_README if you need to build Postfix with a specific library.

Visible differences: some error messages may have a different text,
and the 'X' pattern flag is no longer supported with pcre2.

Major changes with snapshot 20210815
====================================

Updated defense against remote clients or servers that 'trickle'
SMTP or LMTP traffc. The new {smtpd,smtp,lmtp}_per_request_deadline
parameters replace {smtpd,smtp,lmtp}_per_record_deadline, with
backwards compatible default settings. This defense is automatically
enabled by default in the Postfix SMTP server in case of overload.

The new smtpd_per_record_deadline parameter limits the combined
time for the Postfix SMTP server to receive a request and to send
a response, while the new {smtp,lmtp}_per_record_deadline parameters
limit the combined time for the Postfix SMTP or LMTP client to send
a request and to receive a response.

Additionally, the new smtpd_min_data_rate parameter enforces a
minimum plaintext data transfer rate for DATA and BDAT requests,
but only when smtpd_per_record_deadline is enabled. After a read
operation transfers N plaintext bytes (possibly after TLS decryption),
and after the DATA or BDAT request deadline is decreased by the
elapsed time of that read operation, the DATA or BDAT request
deadline is increased by N/smtpd_min_data_rate seconds. However,
the deadline is never increased beyond the smtpd_timeout value. The
default minimum data rate is 500 (bytes/second) but is still subject
to change.

The new {smtp,lmtp}_min_data_rate parameters enforce the corresponding
minimum DATA transfer rates for the Postfix SMTP and LMTP client.

Major changes with snapshot 20210605
====================================

Support to inline the content of small cidr, pcre, and regexp tables.

Example:

    smtpd_forbidden_commands =
	CONNECT GET POST regexp:{{/^[^A-Z]/ Thrash}}

The basic syntax is:

/etc/postfix/main.cf:
    parameter = .. map-type:{ { rule-1 }, { rule-2 } .. } ..

/etc/postfix/master.cf:
    .. -o { parameter = .. map-type:{ { rule-1 }, { rule-2 } .. } .. } ..

Postfix ignores whitespace after '{' and before '}', and writes each
rule as one text line to an in-memory file: 

in-memory file:
    rule-1
    rule-2
    ..

Postfix parses the result as if it is a file in /etc/postfix.

Note: if a rule contains $, specify $$, to keep Postfix from trying to
do $name expansion as it evaluates the parameter value.