Catch All
https://wiki.zimbra.com/wiki/Managing_Domains
Adding multiple catchalls
zimbra@zimbra:~$ zmprov modifyAccount [email protected] zimbraMailCAtchAllAddress @domain1.com
zimbra@zimbra:~$ zmprov modifyAccount [email protected] +zimbraMailCAtchAllAddress @domain2.com
zimbra@zimbra:~$ zmprov modifyAccount [email protected] +zimbraMailCAtchAllAddress @domain3.com
MTA
https://wiki.zimbra.com/wiki/Sending_mail_through_an_external_relay
SPLIT DOMAIN
https://wiki.zimbra.com/index.php?title=Split_Domain
SET DNS
https://wiki.zimbra.com/wiki/DNS_caching_service_(dnscache)