[__jal]

Other reasons I haven't mentioned:

Using Mutt is the easiest way I've found to get and (more importantly) keep GPG configured. Yes, people use it; in my case, for interacting with some open source projects.

I've played with setting up various graphical clients with it, but I don't use GPG every day, and it somehow always manages to break in some annoying way. Configuring that with Mutt is loosely coupled enough that it just keeps working.

And second, once you're comfortable with your config, triaging huge amounts of mail is blazingly fast. You might not notice the delay that comes from the occasionally slow GUI reactions, intentionally slow animations, dialogs, the mouse, etc. But compared to the instant reaction to single character commands, there's no contest, and if you're catching up on an enormous amount of mail for some reason, it really makes a difference.

And if you ever have to deal with automated mail systems that succumb to sudden-onset logorrhea in your direction, regular expressions for tagging mail for group operations are a godsend.