msmtp is an SMTP client.

In the default mode, it transmits a mail to an SMTP server 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:

- Sendmail compatible interface (command line options and exit codes)
- Support for multiple accounts
- TLS/SSL support including client certificates
- Support for Internationalized Domain Names (IDN)
- Many authentication methods
- Fast SMTP implementation using command pipelining
- DSN (Delivery Status Notification) support
- SOCKS proxy support

Homepage:
https://marlam.de/msmtp/
