When I first started using Linux a GUI was something I rarely used because the GUI was incredibly slow for system administraton. A lot has changed over the years, but my need for quick and simple tools has not.
I do a lot of work on my server via ssh. There are times when I check email local to my server via ssh. In my humble opinion the best tool for checking email via command line is Pine.
A few years back Red Hat (among others) discontinued shipping Pine because of incompatabilities with U.W. licensing and the GPL. See the U.W. Pine Legal FAQ for more information.
To me Pine ranks up there as one of the very best command line tools ever created. It’s such a shame that our GUI culture has pushed tools such as Pine to the back burner.