Outlook 2010 password prompt for Exchange Online, O365 public folders
Posted by rbTech Staff on 03 August 2016 12:02 PM

We tripped over a good one this week, and the resolution was simple, even though the troubleshooting steps were long and arduous.


Background: SBS 2008 site migrating email to Exchange Online (O365).  Endpoints have Office 2010 installed, fully service packed (SP2 as of this writing).

We did all the usual prep for migrating to Exchange online including changing internal and external DNS to have proper autodiscover records, etc.., and the migration had been performed successfully.  However, because we're cautious types, we always run the on prem Exchange server running for a week or so until we're satisfied that there's no need for the data anymore, and it's all 100% moved.

The mailbox would connect up to O365 just fine, but then Outlook was continually prompting for a password for the user, and Public folders were not working right.

The Exchange connectivity analyser reported that things were working OK, but when we used the Outlook Autodiscovery Testing (right-click the Outlook icon in the System Tray, click "Test Email Autoconfiguration) it was failing on a non-existent domain lookup.

This prompted a search through AD for the culprit, which turned out to be the ClientAccessServer URI configured by SBS.

In the Exchange Management Shell on the old Exchange server, run:

[PS] C:\> Get-ClientAccessServer -Identity SERVERNAME | fl *uri*

This will return a value that probably matches the 401 error returned in the Outlook Autodiscovery Testing tool, and it will need to be zeroed out:

[PS] C:\> Set-ClientAccessServer -Identity SERVERNAME -AutoDiscoverServerInternalUri $null

Once we did that, Outlook stopped prompting for password and all was right with the world again (and most importantly, users were able to get to their Public Folders without issue!).

Thanks to Walvis from Microsoft O365 support for the assist - he got me looking in the right direction for this.



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