I installed zimbra on a ubuntu 8.04 machine no issues everything went well. After installation I could send mail with no issues. I also when into global settings>Mta and I unchecked Protocols and DNS Check (Below).
Hostname in greeting violates RFC
Client must greet with a fully qualified hostname
Sender address must be fully qualified
Client's IP address
Hostname in greeting
Also in severs>Mta enable DNS lookups. I did that from reading a forums it helped someone. That obviously did not help me. So I set them all back, and not I can receive mail. Can someone explain what these are and how to get to the bottom of sending and receiving?