There are always games hosted on Dom3Minions.com
http://www.dom3minions.com/HostedGames.htm
Most are small. 1-4 players. You can pick one and create a thread here saying "game at xxxxxx, come and join me!".
But they arent pbem. They are direct-connect games which play alot like solo games, but with multiple players. The simplest would be the Blitz games, and then maybe the vsAI which is blitz with computer players tossed in.