If you see an error like this:
Error: 554.Relay access denied. Mail could not be sent. Recipient address rejected.
Your email settings are probably not setup correctly. This error usually occurs when your outgoing server (SMTP) settings do not include a login. Open up your account settings in your email program and make sure that you have your username and password entered into the outgoing server settings. Sometimes you can check a box to use the same login as the incoming server.