I"m getting a "relay denied" error message when trying to send my mail.

You attempt to send mail, but receive an error message that looks like this: protocol smtp; server response 550; relay attempt failed

In order to prevent our mail servers from being used for the transmission of SPAM, we've configured our servers to require that no mail can be sent from a given domain's SMTP (outgoing mail) server unless you authenticate yourself.

You need to setup your mail server to require authentication of your outgoing emails and provide the same username and password as used for your incoming email.