There is a (new! exciting!) feature for 1.5 that gives us email bounce handling so that users with bad email addresses are forced to change them, and opens the door for integrating new stuff like mail-to-forums interfaces.
The code is in HEAD now, and I've written instructions on how to configure your email server (MTA) to hook into the new functionality. We are looking for testers keen on trying the new code and helping is make the setup instructions better.
You need * a unix-y OS (MacOSX, Linux, Solaris, etc) * a reasonable understanding of your MTA * root access