Univention Corporate Server 4.1 erratum 18 (bugfix)

This update addresses the following issues:
* An error in the dovecot listener could lead to the unintended
  deletion of a shared folder if the corresponding LDAP objects is changed
  (Bug 40014).
* The UMC permissions "write" and "all" for shared folders did not
  contain the IMAP permission for expunge. A removal of mails or moving
  mails was not possible. This problem has been fixed and the permission
  will be updated automatically if the join script of
  univention-mail-dovecot is called.