I'm working on a modal, console-based, email-client. It's developed in C++ and has fully integrated scripting provided via lua.
https://github.com/skx/lumail/
It is pretty different from the existing mail clients for the console (pine, alpine, mutt, sup, notmuch), partly for being modal, and partly because it only handles Maildirs. No IMAP or POP3 support at all.
In terms of functionality it is usable for sending, processing, and receiving emails. But there is still missing support for attachments.