Postfix packages older than 2.2.4-5mdk had a wrong triggerpostun script
which made it difficult to change the alternatives scheme.

Starting with 2.2.4-6mdk a new alternatives scheme is being used which is
described best here: http://archives.mandrakelinux.com/cooker/2005-06/msg01987.php

This introduced problems in the upgrade due to that old triggerpostun script.
The main symptoms are broken symbolic links and missing binaries (like
/usr/bin/mailq).

Not all upgrades will have this problem: just the ones where a postfix package
with the broken triggerpostun script is upgraded directly to postfix >= 2.2.4-6mdk.

The init script in postfix >= 2.2.4-6mdk will correct most of the problems as soon
as the service is (re)started, but the following manpages will not be accessible: 
mailq(1), newaliases(1) and aliases(5).

A reinstallation of the postfix package (or any further upgrade) will fix
all issues.

See the http://archives.mandrivalinux.com/cooker/2005-07/msg01012.php thread
for a more detailed explanation.