User Unknown

----- The following addresses had permanent fatal errors -----
<JDOE@YOURDOMAIN.COM>
(reason: 550 5.1.1 <SBEMIS1@YOURDOMAIN.COM>... User unknown)

----- Transcript of session follows -----
... while talking to mx-rr.home.com.:
>>> RCPT To:<JDOE@YOURDOMAIN.COM>
<<< 550 5.1.1 <JDOE@YOURDOMAIN.COM>... User unknown
550 5.1.1 <JDOE@YOURDOMAIN.COM>... User unknown

Instead of "user unknown", you might see "unknown user", "invalid recipient", "not a valid user", "mailbox unavailable", "not known here" or something else expressing the same idea.

In this example our mail server tried to deliver the message to the mail server at home.com, but the yourdomain.com mail server refused to accept it because they have no user known as "jdoe". This could be because the username part of the address (jdoe) was typed incorrectly, or because the "jdoe" account at home.com expired or was cancelled, or because you were trying to reply to a message sent out under a falsified address. In rare cases it can indicate a mail system failure at the remote site.

What you should do:

Confirm the intended recipient's address, if possible. Resend your message to the corrected address.

We accept: