On this notebook computer, I am using/testing Evolution as MUA (Mail Transfer Agent). When I compose e-mail, it is done by Evolution and Emacsclient.
But, I need to send e-mail by command line sometimes.
For those cases, I installed a package named 'ssmtp'.
The configuration is like this.
mailhub=atom.fsij.org:465 rewriteDomain=fsij.org hostname=latx1.gniibe.org FromLineOverride=YES UseTLS=YES AuthUser=<USERNAME> AuthPass=<PASSWORD> AuthMethod=cram-md5
See MTA settings accepting SSMTP for submission for server side settings.