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We have Exchange 2010 with EdgeTransport.

I have created a new user for the first time in months and this user works fine internally. But externally, any inbound email for the user gets rejected with "550 user unknown".

I've tried various things like comparing the user settings to a "known good" user. And start-edgesynchronization etc. Nothing works.

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Sure it's not happening at the forwarding/hosting provider level instead of at the Exchange level? – HaydnWVN Dec 6 '11 at 11:37
No we don't have anyone else in the loop. The MX record hits the EdgeTransport directly. – J.B. Dec 6 '11 at 12:06
I don't know anything about EdgeTransport, and havn't used Exchange since Windows Server 2003, so for that reason i'm out (and i really shouldn't watch so much Dragons Den). – HaydnWVN Dec 6 '11 at 12:40

Per, uncheck the "Require that all senders are authenticated" field on the user.

We just had a similar issue with the Recipient Filtering feature of Exchange’s anti-spam functionality (see which we had to turn off until we find why users are not working properly.

-- teeje

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