Fresh minimal install of CentOS4.4. Install of Zimbra completes without error. I can login to the admin console and create user accounts. I can login to those accounts. When I try to send any email from those accounts, even from: foo@<domain> to foo@<domain>, I get bounce messages with errors messages such as:
mail for <domain> loops back to myself.
DNS has been configured such that both the domain and the hostname of the mail server have an MX RR that points to the mail server itself.