Zimbra Outgoing SMTP IP per Domain 1. Add the following line in “/opt/zimbra/postfix/conf/main.cf” sender_dependent_default_transport_maps = regexp:/opt/zimbra/postfix/conf/sdd_transport_maps.regexp 2. Create the file “/opt/zimbra/postfix/conf/sdd_transport_maps.regexp” and add the domains as below /@example\.com$/ …