Old school choice: nmh[0]. It is a very different way of interacting with email. From section 1.2.1[1]:
Because MH commands aren't part of a monolithic
mail system, you can use them at any time; you
don't have to start or quit the mail agent.
It's fine to mix other UNIX commands between
your MH commands, to leave your mail for a
while and do something else, and to work at
several terminals at the same time. Because
you use MH commands from a shell prompt, you
can use all the power of the shell.
I've used Postfix+fetchmail successfully, but am going to look into "msmtp" mentioned by @gkya above as it is new to me.
Also, OfflineIMAP[0] looks to be a solid IMAP solution, which may replace my use of fetchmail. However, a maintainer of OfflineIMAP indicates he is focused on imapfw[1]. So maybe that's one to look into as well. It's not that I'm unhappy with fetchmail, but it doesn't hurt to know what the relative strengths and weaknesses are of the choices available.
1 - http://rand-mh.sourceforge.net/book/overall/howwor.html#EmaT...