ssmtp binary package in Ubuntu Bionic amd64

 A secure, effective and simple way of getting mail off a system to your
 mail hub. It contains no suid-binaries or other dangerous things - no mail
 spool to poke around in, and no daemons running in the background. Mail is
 simply forwarded to the configured mailhost. Extremely easy configuration.
 .
 WARNING: the above is all it does; it does not receive mail, expand aliases
 or manage a queue. That belongs on a mail hub with a system administrator.

Source package