 What access method?
If you're using the web client only, set the webservers SMTP host to be your main mail server - that will deliver all mail to that server, and anything for zimbra will be forwarded back.
If you've got POP or IMAP users, make them use the main mail server for SMTP.
You can also set the relay_host on the zimbra server to point to your main mail server - that should cover everything, as long as noone is using the zimbra server for SMTP (except the main mail server, which will only connect for accounts that live in zimbra.) |