sSMTP is a simple SMTP client for sending mail from your local client to a mail hub with a more serious MTA. For example, my main server is running Postfix, but I want to send mail from my laptop. I use sSMTP to do this.

Before you use sSMTP, you need to configure it so it knows how to connect to the mail hub. My /etc/ssmtp/ssmtp.conf is:

root=jdoe
mailhub=mail.example.net
rewriteDomain=example.com

This sends mail via mail.example.net, and replaces my current domain name with example.com. jdoe@mail.example.net will recieve all system-generated email (i.e. cron job output).

There are other settings available in the config file. The stock config contains lots of comments explaining how to use them, and the ssmtp.conf man page contains even more details.

I felt like the SSL/TLS handling for sSMTP was a bit sparse (for example, it doesn't validate the server certificate), so I've submitted some patches upstream (662958 and 662960).

If sSMTP doesn't scratch your itch, the next level up in terms of features is msmtp, which I used to use before I setup my own mail hub.