I've just got ZCS Open Source Edition up and running on Ubuntu 10.04 LTS. It all appears to have installed correctly. I'm also using ASSP as an external relay, running on a separate machine.
This set up receives mail fine, however when sending outbound emails to external addresses, I get the error:
(external yahoo email address): mail for mail.mydomain.com:25 loops back to myself
The ASSP machine listens on port 25 and forwards to the Zimbra machine's IP address on it's port 25. The ASSP machine has an MX record in mydomain.com; the Zimbra one doesn't (only an A NAME). Both machines have externally-facing IP addresses.
In the Zimbra Admin console, under Global Settings > MTA, the "Network" section is as follows:
"Webmail MTA Host Names" has the FQDN (i.e. mail.mydomain.com) of the Zimbra machine and the port is showing as 25.
"Relay MTA for external delivery" is set to the FQDN for the ASSP machine on port 25
"Inbound SMTP host name" is also set to the FQDN of the ASSP machine.
"MTA Trusted Networks" is empty and "Enable DNS Lookups" is checked.
I'm assuming there probably something simple but not obvious which is causing Zimbra to find this loop. I'm a bit of a Zimbra noob so any pointers would be greatly appreciated.
Thanks in advance,