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I get a - 550 5.1.1 User unknown; rejecting - message

When you try to send an e-mail, you get an immediate "550 5.1.1 User unknown; rejecting" message.  However, you know the account you're sending to exists and have no problems sending mail to it from other hosts.

This problem usually occurs when you have setup a full domain on our servers with the same name as the domain you're trying to send to.  Our mail server will try to send mail locally first.  If it finds the domain locally, it looks there for the mailbox, and if it doesn't find the mailbox, it sends back a user unknown message.  The process stops there.

To prevent this problem, you will need to delete the domain from our servers.

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