msmtp is an SMTP client.

In the default mode, it transmits a mail to an SMTP server (for example at a free mail provider) which takes care of further delivery.
To use this program with your mail user agent (MUA), create a configuration file with your mail account(s) and tell your MUA to call msmtp instead of /usr/sbin/sendmail.

Features include:

msmtp is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3 of the License, or (at your option) any later version.