smtp-cli is a powerful SMTP command line client with a support for
advanced features, such as STARTTLS, SMTP-AUTH, or IPv6 and with a
scriptable message composition capabilities supporting anything
from simple plain-text messages right up to building complex HTML
emails with alternative plain-text part, attachments and inline
images. The MIME-Type of the attachments can either be guessed
automatically or alternatively set on the command line, separately
for each attachment if required.

WWW: http://www.logix.cz/michal/devel/smtp-cli/