S-nail (later S-mailx) provides a simple and friendly environment for
sending and receiving mail.  It is intended to provide the functionality
of the POSIX mailx(1) command, but is MIME capable and optionally offers
extensions for line editing, S/MIME, SMTP and POP3, among others.
It divides incoming mail into its constituent messages and allows the
user to deal with them in any order, offers many commands and variables
for manipulating messages and sending mail, as well as line editing, and
increasingly powerful scripting capabilities.

Homepage:
https://www.sdaoden.eu/code.html
