Univention Corporate Server 4.2 erratum 288 (bugfix)

This update addresses the following issues:
* The listfilter policy service can now write debugging information to the
  mail log, when the UCR variable mail/postfix/policy/listfilter/debug is
  set to "yes" (Bug #44922).
* The content of the files main.cf.local and master.cf.local will now be
  appended to /etc/postfix/main.cf and /etc/postfix/master.cf respectively.
  After editing the *.local files, ucr commit /etc/postfix/*.cf must be
  called (Bug #44473).
* If mail/postfix/policy/listfilter/use_sasl_username=yes was set, the
  listfilter policy service rejected all mail unexpectedly. The listfilter
  policy service has been fixed and now handles Cyrus SASL authentication
  correctly (Bug #45422).
* Postfix' service postscreen has been integrated and can be configured
  via the UCR variables prefixed by mail/postfix/postscreen/. The service
  performs lightweight checks on incoming SMTP connections to reject e.g.
  spam early (Bug #45607).