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Anyone outside my domain who sends me an email is getting a bounced email with the following error from Exchange:

550 550 5.1.1 is not a valid mailbox (state 14).

I can't receive emails from external addresses until I send an email to one of my secondary addresses. Once I sent it to my secondary address, my primary address will start working for a while and fail again after a few hours.

We use Exchange 2003. Anyone has any suggestions on what to try?

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That doesn't look like an Exchange 2003 NDR. What's the reporting MTA in the NDR? Do you use a third party filter in front of the Exchange server or on the Exchange server?

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