+ 0 Votes SMTP Authentication blazinride 7 years ago The SMTP server is telling you that it cannot relay for that user. Did you have relay authentication set up for that SMTP server via computer accounts instead of user accounts? I would check your relay settings on the SMTP server. Is that message coming from your internal mail server, or your isp's server? If its coming from your ISP's mail server, it may be a problem with the email address. + 0 Votes SMTP Authentication Mickster269 7 years ago It's coming from our internal mail server. The message never gets out of the building. We CAN email inside the domain. We have found out (so far) that if we assign the computer a static public IP, it can send mail. I will check into how the Authentication is set up (user vs computer)- thanks for the tip!