Univention Corporate Server 4.2 erratum 36 (bugfix)

This update addresses the following issues:
* Support for forwarding user emails to external addresses has been
  added. During the update, the UCR variables
  mail/postfix/virtual/alias/maps and
  mail/postfix/virtual/mailbox/maps are updated automatically,
  because some postfix virtual lookup tables have been modified.
  Please note, that the forwarding of emails on systems with OX App Suite
  will only come into effect if at least version 7.8.3-ucs2 of OX App
  Suite is installed (Bug #42249).
* The default of the UCR variable mail/postfix/tls/client/level when
  unset has been changed to "may". On existing UCS installations this
  has already been set explicitly (Bug #44589).
* When a relay host with authentication is used (mail/relayauth=yes),
  the Postfix option smtp_tls_security_level will automatically be set
  to "encrypt", unless mail/postfix/tls/client/level is set to "none"
  (Bug #44589).