Undelivered Mail Returned to Sender

This is the Postfix program at host mx1.watchguard.com.

I'm sorry to have to inform you that the message returned
below could not be delivered to one or more destinations.

For further assistance, please send mail to <postmaster>

If you do so, please include this problem report. You can
delete your own text from the message returned below.

			The Postfix program

[off-list ref]: host 127.0.0.1[127.0.0.1] said: 550 5.7.0 Message
    content rejected, id=10402-05