Another new aggregation program called Hep looks promising. It plans to integrate both pop/smtp mail, a webservice and jabber support to allow posting/reading of weblogs. No MT support yet though :(
Hep Message Server is software that transfers bits of information between different messaging sytems on the Internet. When it's done, you'll be able to use Hep to transparently route messages between e-mail, weblogs, and instant messaging.