I’d love to know why Zimbra does not ship with recipient verify turned on. Here’s the use case: a user sends a message from the web interface with an invalid recipient. He/she does not get an error when the message is sent but instead receives an immediate bounce. Sure the info is in the bounce but it’s easy to miss in a cluttered inbox and it’s a hassle to parse.

The solution is very simple. On each host running postfix:

As zimbra:

$ vi /opt/zimbra/postfix/conf/main.cf
relay_recipient_maps = ldap:/opt/zimbra/conf/ldap-vam.cf
$ vi /opt/zimbra/conf/zmmta.cf
POSTCONF smtpd_reject_unlisted_recipient yes
$ zmmtactl restart

This works in zcs 5.0.x and 6.0.6. It will likely work in other versions as well.