I've got avast configured on my mail server as a proxy, so avast gets my mail, then passes it to the server. This setup works just fine, but only because my mail server uses relay security that's based on username/password. Unfortunately, avast passes MY ip address as the originating ip address to the server. Reverse dns blacklists or anything else based on originating ip address won't work right because the originating IP address is that of the mail server machine.
I'm not familiar with dmail - I use MailEnable.
It's not at all hard to set up -- there's an excellent how to on these forums for the changes you'll make to avast4.ini ( see
http://forum.avast.com/index.php?board=2;action=display;threadid=1647 )
basically you just have to sent the ip address it listens on, both for smtp and for pop
If you have any problems write back and ask, I'll be glad to help, provided this weeks hurricane leaves me intact (in Florida, usa)
Bill