Sendmail

Create a file with your email:

To: my@email.com
Subject: sendmail test two
From: me@myserver.com

And here goes the e-mail body, test test test..

sendmail -vt < ~/mail.txt

Swaks (SMTP Swiss Army Knife)

echo "This is the message body" | swaks --to rafael.herrero.contractor@bbva.com --from "rraboards@dyndns.org" --server in-v3.mailjet.com --auth LOGIN --auth-user "9******fe" --auth-password "8e1********fc" -tls