The stable Postfix release is called postfix-2.6.x where 2=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-2.7-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 2.5 or earlier, read RELEASE_NOTES-2.6
before proceeding.

Incompatibility with snapshot 20090619-nonprod
==============================================

NOTE: You must stop and start the Postfix master daemon before you
can use the postscreen(8) daemon.  This is needed because the Postfix
2.[56] "pass" master service type did not work reliably on some
systems.

Major changes with snapshot 20090619-nonprod
============================================

Prototype postscreen(8) server that runs a number of time-consuming
checks in parallel for all incoming SMTP connections.  It detects
clients that start talking too soon, or clients that appear on DNS
blocklists, or clients that hang up without sending any command.

By doing these checks in a single postscreen(8) process, Postfix
can avoid wasting one SMTP server process per connection. A side
benefit of postscreen(8)'s DNSBL lookups is that records are already
cached before the Postfix SMTP server looks them up later.

postscreen(8) maintains a cache of positive decisions. Once a client
decision is cached, the client is immediately forwarded to a real
Postfix SMTP server process without further checking.

By default, the program logs only statistics, but it can be configured
to drop clients that start talking too soon, or clients that appear
on DNS blocklists. The logging function is already useful for
research, but the blocking functions are still unpolished.

postscreen(8) has been tested on a limited scale on FreeBSD and
Linux systems. It probably needs additional work before it can be
used on Solaris.

This non-production snapshot adds three new entries to the master.cf
file. 

To enable the postscreen(8) service and log client information
without blocking mail:

- Comment out the "smtp  inet ... smtpd" service in master.cf.

- Uncomment the new "smtp  unix ... smtpd" service in master.cf.

- Uncomment the the new "smtp inet ... postscreen" service in
  master.cf.

- Uncomment the new "dnsblog  unix ... dnsblog" service in master.cf.
  This service does DNSBL lookups for postscreen(8) and logs results.

- To enable DNSBL lookups, list some DNS blocklist sites in main.cf,
  e.g., "postscreen_dnsbl_sites = zen.spamhaus.org".  Separate domain
  names with comma or whitespace.

Note: you must stop and start the master daemon if you are running
a normal Postfix 2.7 snapshot, or an older Postfix version.  This
is needed because the Postfix 2.[56] "pass" master service type did
not work reliably on all systems.

To use the postscreen(8) service to block mail, edit main.cf and
specify one or more of:

- "postscreen_greet_action = drop", to drop clients that talk before
  their turn. This alone stops about one third of all known-to-be
  illegitimate connections to Wietse's mail server.

- "postscreen_hangup_action = drop", to waste no time on clients
  that hang up without sending a command. On Wietse's server, only
  one percent of illegitimate connections behaves like this.

- "postscreen_dnsbl_action = drop", to drop clients that are on DNS
  blocklists. Different blocklists cover different client categories.

Note: right now, these actions drop client connections without
reporting sender and recipient information. In a future version,
the connection may instead be passed to a dummy SMTP protocol engine
that logs sender and recipient information before dropping the connection.

Incompatibility with snapshot 20090606
======================================

The "postmulti -e destroy" command no longer attempts to remove
files that are created AFTER "postmulti -e create".  It still works
as expected immediately after creating an instance by mistake.
Trying to automatically remove other files is too risky because
Postfix-owned directories are by design not trusted.

Major changes with snapshot 20090606
====================================

Support for header checks on Milter-generated message headers.  This
can be used, for example, to control mail flow with Milter-generated
headers with indicators for badness or goodness. For details, see
the postconf(5) section for "milter_header_checks". Currently, all
header_checks features are implemented except PREPEND.