I setup an account for authentication: firstname.lastname@example.org. Mail for the xxxx.com domain is hosted elsewhere. When the contact form sends mail to an address outside of the domain, it works fine. When the contact form send mail to a valid address - email@example.com - which is hosted on a different service, I get an error message. Apparently SmarterMail thinks it will deliver locally, but sees it doesn't have that account. How can I tell SMTP to just pass the message along? The error message is: Mailbox unavailable. The server response was: <firstname.lastname@example.org> No such user here where email@example.com is the recipient's address, not the authentication address. If I add a BCC to the message, the BCC is received, even though I get this error message. The message to firstname.lastname@example.org is not received.