Text: Mutt, Alpine, and emacs's mailer off the top of my head. There's a listing of other clients here: <https://www.tecmint.com/best-commandline-email-clients-for-l...>
GUI: Sylpheed, Thunderbird, KMail (KDE's Kontact suite still strikes me as one of the best I've encountered), Evolution, and Clawsmail.
My own strong preference remains mutt, and the ability to process huge amounts of complex email reasonably well is still utterly unmatched.
