I've been researching MUAs (mail user agents) again. I use Mail.app on OS X but would prefer to access email from emacs. I've made several valiant attempts at GNUs but have never been able to get into it, partly due to it's mediocre (IMO) support for SMTP. It looks like there's renewed interest in the project by one of the original developers and there's lots of new activity. I'll try it again.
In the meantime I'm looking at other emacs-friendly MUAs. MH-E (mail handler for emacs) has caught my attention before. Mail Handler (mh or nmh) really appeals to the Unix-way purist in me: lots of little utilities that do one thing extremely well. MH-E is an emacs wrapper for the mh utilities that brings the power of mh to your favorite text editor.
While re-acquainting myself with mh I found this seriously titled article "How to Process 200 Emails per Day and Still Get Some Real Work Done" (Note: It's a postscript file). I laughed at the title because I know people who'd be happy to get a mere 200 emails per day. Still, it's an interesting read if you're interested in mh. Non-mh users might be able to find useful tidbits to help with inbox processing but not many.