twice in the last week i have needed to send a quick email from the command line. here’s how:

telnet 1.2.3.4 25

HELO domain.name
MAIL FROM: [email protected]
RCPT TO: [email protected]
DATA
Subject:subject line here

this is the
body of your
email.
.
QUIT

note: there has to be a blank line under the subject line.

source: http://www.yuki-onna.co.uk/email/smtp.html