Mutt's own SMTP:

Starting with version 1.5.17, mutt now - miracle of miracles - has the capability of sending your messages without the need for another program like sendmail. This goes essentially against the mutt philosophy, but was requested by enough users that the decision was made to include SMTP capability. To take advantage of this, in your muttrc file you would add your log in information in the following format:

set smtp_url="smtp[s]://[user[:pass]@]host[:port]/"

Let's say you have a mail account whose SMTP address is outmail.mailhost.com, where you log in using the name `squeaker' with password `bear.'

set smtp_url="smtp://squeaker:bear@outmail.mailhost.com"