What is a Mail Relay Denied Error?

Here is an explanation of mail relay errors.
Basically, our mail server will only send mail out for our clients. The way that our server can tell that you are a client is by your e-mail address.

Check your mail settings to make sure that your e-mail address is in the form (username)@wonderwave.net. POP and SMTP mail servers should be set to mail.wonderwave.net.

If you need to have two different mail accounts set up, all the settings for each of the accounts should show the same domain name (for example "wonderwave.net").

ISSUE: When sending mail in Eudora, the error message "550 Relay Denied" is given by the SMTP server (Eudora may display "This message is not acceptable to your SMTP server. The message is not sendable until the recipient has been changed.") and mail cannot go out.

SOLUTION: Service Providers have moved toward restricting access to their outgoing mail servers to provide better service to their customers and prevent SPAM from being sent through their mail servers. There are different methods for establishing restrictions that could result in you being denied access to your outgoing mail server.

When you connect to a mail server and send mail that is going to another mail server on another domain, that is called mail relay. Historically, SMTP servers did not check to verify that the sender was who he claimed to be and would simply pass the mail on with whatever return address was specified, no questions asked. Unsolicited bulk mailers have taken advantage of this to send huge volumes of mail with bogus return addresses (which slows down the server for the paying customers who have the right to use it, slows down servers everywhere with all that junk mail, and makes people mad at the ISP for allowing the bulk mail to cause such problems to be sent through their outgoing server).