on this page:
in the email management section, the post:
Example contact form (form-to-mail).
gives an example of sending an email using php mail.
it looks like the smtp server and port should be left blank.
note in the example:
$myemail = "email@example.com"; Caution: replace firstname.lastname@example.org with a vaild one you created in Email Manager
this is the to address. So it sounds like they will only allow you to send emails that are going to an email you register for your domain. It sounds like they do not allow for outgoing email traffic to other domains.
you may want to look into another host that is not so restrictive with sending emails. I use 1 and 1 and have very good experience with them.