Also, I'm trying to set up zapgun.net as the deafult domain. The instructions I have seen so far only say how to set it up with a host name mailserver.zapgun.net which means the default address become firstname.lastname@example.org
I changed all the settings from mailserver.zapgun.net to just zapgun.net (which means the hosts file is missing the host name). It seemed to install ok but the antivirus service stopped working and the messages were held in the deferred queue. Can any one tell me if they've installed it with out a hostname.