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 20091008
======================================

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

Major changes with snapshot 20091008
====================================

Prototype postscreen(8) server that runs a number of time-consuming
checks in parallel for all incoming SMTP connections, before clients
are allowed to talk to a real Postfix SMTP server.  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 DNS records are
already cached before the Postfix SMTP server looks them up later.

postscreen(8) maintains a temporary whitelist of positive decisions.
Once an SMTP client is whitelisted, it is immediately forwarded
to a real Postfix SMTP server process without further checking.

By default, the program logs only statistics, and it does not run
any checks on clients in mynetworks (primarily, to avoid problems
with buggy SMTP implementations in network appliances).  The logging
function alone is already useful for research.

postscreen(8) can be configured to drop clients that start talking
too soon, or clients that appear on DNS blocklists. For details,
see below.

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

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

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

1 - Comment out the "smtp  inet ... smtpd" service in master.cf,
    including any "-o parameter=value" entries that follow.

2 - Uncomment the new "smtpd pass ... smtpd" service in master.cf.

3 - Uncomment the the new "smtp inet ... postscreen" service in
    master.cf, and duplicate any "-o parameter=value" entries from
    the smtpd service that was commented out in step 1.

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

5 - 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.  This is needed
because the Postfix "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.

There is also support for permanent blacklists and whitelists; see
the postscreen(8) manual page for details.

Note: right now, postscreen(8) "drop" actions disconnect the client
without reporting sender and recipient information. In a future
implementation, 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.