Bounce with Recipient rejected by the SMTP Server message?

This error usually occurs when one or more of the recipients of your e-mail message has an invalid e-mail address. For example, if you forget to put an “@” in the e-mail address, the SMTP server will automatically reject the message and it will not be sent. You will need to look at the recipient or recipients of your e-mail and make sure the syntax (username@yourdomain.com) is correct.