Outlook prompts for credentials after turning off old Exchange 2003 server

We have a customer who we are migrating from SBS 2003 to Server 2012 with Exchange 2010. All mailboxes and public folders have been migrated to Exchange 2010, and all inbound SMTP email is being delivered to Exchange 2010. So far so good.

Yesterday evening, I stopped all of the Exchange 2003 services on the SBS. I sent test emails in and checked that they had arrived using OWA and Outlook 2003 (I have a domain admin account).

This morning, the customer phoned to say that some user's Outlook is prompting for credentials.

As soon as I enable all Exchange 2003 services, the problem goes away!

I'd like to decommission Exchange 2003, so any help would be appreciated.

Thank you.
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Chris MillardAsked:
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Shreedhar EtteCommented:
Make sure that Exchange 2010 databases are pointing to Public Folder on Exchange 2010.

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Chris MillardAuthor Commented:
Thanks - I have now done as you suggested (it was pointing to the Exchange 2003 server). I'm just awaiting authorisation to turn off Exchange 2003 again to test, so will report back shortly.
Simon Butler (Sembee)ConsultantCommented:
Turning off Exchange to confirm things continue to work correctly isn't really a valid test.
Exchange expects all servers to be available and will throw errors when they are not. I don't even bother with the test when doing a migration because it tells me nothing.
You need to remove Exchange using add/remove programs then clean up the mess afterwards. Nothing else works. If you have followed the numerous guides for migrating Exchange, then that shouldn't cause much of a problem.

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