Inzwischen weiß ich das es etwas mit dem LDAP Server zu tun hat.
Im Zarafa log unter server.log steht:
Cannot instantiate user plugin: Failure connecting any of the LDAP servers
Unable to instantiate user plugin
listener.log
10.02.16 09:19:57.028 LISTENER ( WARN ) : can not connect any server, retrying in 30 seconds
10.02.16 09:20:27.028 LISTENER ( WARN ) : chosen server: ucs.mail-ta.local:7389
10.02.16 09:22:34.211 LDAP ( ERROR ) : start_tls: Can't contact LDAP server
10.02.16 09:22:34.212 LISTENER ( WARN ) : can not connect to LDAP server ucs.mail-ta.local:7389
10.02.16 09:22:34.212 LISTENER ( WARN ) : can not connect any server, retrying in 30 seconds
10.02.16 09:23:04.212 LISTENER ( WARN ) : chosen server: ucs.mail-ta.local:7389
10.02.16 09:24:16.567 LISTENER ( WARN ) : received signal 15
10.02.16 09:30:43.875 DEBUG_INIT
10.02.16 09:32:51.143 LDAP ( ERROR ) : start_tls: Can't contact LDAP server
10.02.16 09:32:51.143 LISTENER ( WARN ) : can not connect to LDAP server ucs.mail-ta.local:7389
10.02.16 09:32:51.143 LISTENER ( WARN ) : can not connect any server, retrying in 30 seconds
10.02.16 09:33:21.144 LISTENER ( WARN ) : chosen server: ucs.mail-ta.local:7389