Problem with Outlook constantly prompting for password

Hi - we are using Rackspace hosted exchange, and for the last few weeks we've had this problem that we cant resolve. For some reason, for a couple different email addresses, on a couple different computers, we are constantly getting pop-ups in Outlook 2016 and 2010 looking for a password for the email accounts. The accounts are and have been set to autodiscover when setting up the email address and this hasn't been an issue for years prior to a few weeks ago. I've created new passwords, created new profiles, removed and added cached mode, but nothing seems to be working, and Rackspace has no answers. Any help would be appreciated.
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FOXActive Directory/Exchange EngineerCommented:
Please test one workstation doing the following-
1. Go in to Control Panel>Credential Manager>Windows Credentials and remove all the saved passwords in there
2. Remove any passwords that have been saved on the browsers of this workstation as well
3. Close outlook and then reopen it in safe mode - in the run box type in      outlook /safe      press Enter
4.  When it prompts for credentials put in the user's credentials and password and put a check in "Remember Credentials"
Marco van BeekManaging DirectorCommented:
This can happen when the wrong authentication is set (or being used) and/or autodiscover isn't set up properly. With NTLM authentication Exchange is expecting the domain name, and if the Exchange server and the workstation Outlook is on are not in the same domain, the desktop with send whatever domain it is in. At a guess you are using Outlook Anywhere rather than tunnelling over a VPN so Kerberos/MAPI isn't fixing the problem in the background for you.

I would try changing the Outlook Anywhere authentication method to basic, but first use the Microsoft Remote Connectivity Analyser ( and test both Autodiscover and Outlook connectivity and make sure they are working as expected.

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