When you are using the Zimbra mail server behind NAT with Split DNS, you need to disable dnscache service.
To view all enabled/installed services, run
zmprov gs `zmhostname` zimbraServiceEnabled zimbraServiceInstalled
Example
zimbra@mail:~$ zmprov gs `zmhostname` zimbraServiceEnabled zimbraServiceInstalled # name mail.serverok.in zimbraServiceEnabled: amavis zimbraServiceEnabled: antivirus zimbraServiceEnabled: antispam zimbraServiceEnabled: opendkim zimbraServiceEnabled: logger zimbraServiceEnabled: ldap zimbraServiceEnabled: mta zimbraServiceEnabled: dnscache zimbraServiceEnabled: memcached zimbraServiceEnabled: snmp zimbraServiceEnabled: stats zimbraServiceEnabled: proxy zimbraServiceEnabled: service zimbraServiceEnabled: zimbra zimbraServiceEnabled: zimbraAdmin zimbraServiceEnabled: zimlet zimbraServiceEnabled: mailbox zimbraServiceEnabled: spell zimbraServiceInstalled: amavis zimbraServiceInstalled: antivirus zimbraServiceInstalled: antispam zimbraServiceInstalled: opendkim zimbraServiceInstalled: logger zimbraServiceInstalled: ldap zimbraServiceInstalled: mta zimbraServiceInstalled: dnscache zimbraServiceInstalled: snmp zimbraServiceInstalled: stats zimbraServiceInstalled: memcached zimbraServiceInstalled: proxy zimbraServiceInstalled: mailbox zimbraServiceInstalled: spell zimbra@mail:~$
To disable dnscache service, run
zmprov ms `zmhostname` -zimbraServiceEnabled dnscache zmprov ms `zmhostname` -zimbraServiceInstalled dnscache
Stop dnscache service
zmdnscachectl stop
Stop zimbra
zmcontrol stop
Start Zimbra
zmcontrol start
