Programs: mail clients

Unix

Mail Sending
msmtp	simple smtp server
Mail Storage
offlineimap	synchronize imap, and a local maildir
isync	synchronize imap, and a local maildir
mbsync	synchronize imap, and a local maildir
imapfilter	move/sort email messages into folders (on an imap server)
Mail Authentication
mailctl	renew/authorize OAUTH2 tokens
Contact Management
khard	CLI carddav contacts manager (uses vdirsyncer)
abook	Simple, offline contacts system (integrats with mutt)
baikal	CarDAV server
radicale	CarDAV server (less compliant)
CLI Clients
mutt	CLI based mail client.
neomutt	mutt with several patches applied overtop
meli	mutt-inspired CLI mail client
alpine	CLI based mail client.
GUI Clients
nylas n1	modern mail client. extensible, still under decelopment, cross platform. Beats geary.
geary	mail client
claws mail	good, flexible gui mail client. simple. fast.
thunderbird	Mozilla's mail client. Does not support maildir (no offlineimap)
evolution	Gnome's default mail client (and calendar tool).