Univention Corporate Server 4.1 erratum 87 (bugfix)

This update addresses the following issues:
* Errors when checking restrictions of mailing lists and mail groups are
  now written to the system mail log (Bug 40376).
* The user that wants to send to a restricted mailinglist or group mail is
  now determined using the SASL login. This requires, that the sender logs
  into the server to deliver the email. To enable the previous behavior
  (to use the email address declared by the sender), set the UCR variable
  'mail/postfix/policy/listfilter/use_sasl_username' to "no" (Bug 29615).
* The policy server checking restrictions of mailing lists now exits
  without error, when told to by Postfix (Bug 40569).