Three block sending email using SMTP (TCP port 25) unless it is through their own server. Unfortunately I have found that with emails of more than a few kilobytes in size their SMTP server has a habit of dropping the connection. To work around this you can send to an SMTP server that listens on a different port. One way of doing this is through secure SMTP. If you have a Gmail account you can send email through Google’s server using your login credentials. Just bear in mind that Google’s server may rewrite the “reply to” address of the email to be your Gmail address, so be careful if trying to use this with another email address.
See http://mail.google.com/support/bin/answer.py?hl=en&answer=77689 for more info on configuring Outlook to use Gmail’s SMTP server.