msmtp -- An SMTP client

msmtp is an SMTP client that can be used as an "SMTP plugin" for Mutt and
probably other MUAs (mail user agents). It forwards mails to an SMTP server
(for example at a free mail provider) which does the delivery.
To use this program, create a configuration file with your mail account(s) and
tell your MUA to call msmtp instead of /usr/sbin/sendmail.

Features include:

    * SMTP AUTH methods PLAIN, LOGIN and CRAM-MD5
      (and DIGEST-MD5 and NTLM when compiled with GSASL support)
    * TLS encrypted connections
      (including server certificate verification and the possibility to send
       a client certificate)
    * DSN (Delivery Status Notification) support
    * IPv6 support (on systems that support it)
    * support for multiple accounts
    * sendmail compatible exit codes (which most MUAs understand).

WWW: https://marlam.de/msmtp/