Here is something for everyone who wants to use their ISP as a relay host for outgoing mail. You might want to call it a How to. It took a lot of reading and searching on the zimbra forums, but it was worth it, and it works. Most important make sure that you can send mail internally and receive mail before you continue with this.
Next step is to set your relay MTA to your ISP's mail host and to remove the check from DNS look-up. This is done in the admin console, editing the server
From this point on postfix is your friend, considering you need to add to postfix.
To start you need to enable SMTP authentication on outbound messages: $ postconf -e smtp_sasl_auth_enable=yes
Next is to create a text file mapping which name/password should be used for each given outbound destination:
$ echo mailrelay.example.com usernameassword > opt/zimbra/conf/relay_password this is one line
Create a postfix lookup table
$ postmap /opt/zimbra/conf/relay_password
Test that the map is okay
$ postmap -q mailrelay.example.com /opt/zimbra/conf/relay_password
that should return usernameassword if done right
Make postfix use the above
$ postconf -e smtp_sasl_password_maps=hash:/opt/zimbra/conf/relay_password
Almost done. Two more changes to postfix and then we can send mail externally. We need to change the port we listen on. This is most important for people who use an ISP that does not allow the use of port 25 to listen to ( [I]this is most important for Rogers customers in Canada)
postconf -e relay_host=relayhost.yourisp.com:465
Your ISP might want you to use another port, so check with your ISP for an alternate port.
Restart postfix by entering this
If we try to send mail at this point, we might still get an error (in the zimbra log files would be first place to check):
SASL authentication failure: No worthy mechs found
It took me a while to find the fix for this but here it is:
postconf -e smtp_sasl_security_options=
Thats right nothing after the =. Apparently this option is set to noplaintext,noanonamous by default and that has to be changed.
Once this has been done you just have to restart postfix and we are done.
This should work for all who want to use their ISP as a relay host.
On a personal note, this is the best looking mail server/client that I have found. To all that are working on Zimbra.... KEEP UP THE GOOD WORK.
P.S. I wish I knew when the final release was available, then I could set a timeline to put it into production where I work.