Gnus
In July 2001 I plunged into Gnus. It took a week of experimentation and goofing around to set-up sending email, multiple roles, archive searching, and GPG integration. Next, two days of packing my existing MH folders into mbox format and sorting them over and over again into a new spool area – tweaking the splits each time. This was a part-time endevour; don’t think you’ll need a whole week!
My productivity went up. A bunch. I mean it.
So the first refactoring of my email habits in over 10 years was a resounding success. Since then, I’ve become a Gnus evangelist! I’m constantly trying to convert those around me to use the “Grand Unified Messager(tm)”
My configuration is in the [X]Emacs section.