I can't but help feeling though these days it just doesn't really gain you anything substantive to bother to learn it, or even continue to use it, and spend the hours it will require to dial in and maintain your configuration.
Most gui clients are good enough.. webmail (Gmail and alternatives) are good enough, unless you have some non-negotiable requirement that mandates you have your own self-hosted email servers, I have a hard time believing its not an overall productivity loss to spend time in mutt (or Gnus for emacs, and other such things).
If you like to tinker with that kind of thing, and you like making your email client a hobby of sorts, cool. But what do you really gain other than a techno-bauble to tinker with?
This is my main gripe with mutt. The days where I could futz around with 100 config setting for hours are long behind me. Just having to set up an smtp daemon every time, and having to maintain it, is such a pain in the ass. Probably most tools have moved on by now (I moved away from mutt in 2004 or 2005) but I used mostly postfix and qmail (when I got fed up with one I switched to the other for a few months, etc). Just having to remember the dozens of idiosyncrasies in those was enough of a PITA to make me switch to an integrated graphical mail program.
My main method of searching email was grep -R ~/.Maildir . When I think back about that - ugh.