A user reported that they are receiving multiple credential prompts on their Windows 10 PC in Outlook 2016 for other user mailboxes which he has full access to within Exchange and they are configured to auto mount. Another user in the organization with Outlook 2016 is also configured with full access to one of these mailboxes and does not receive any prompts for it. I began to suspect it was something within his Outlook profile or his mailbox however after making a test user and assigning full access permissions to one of these mailboxes I am seeing the same behavior in Outlook 2016 from my PC.
1. Ran the Outlook Autodiscover connectivity analyzer test and it came back healthy.
2. Cleared the user's credential manager on the PC
3. Putting in the correct username/password for the user mailbox they have full access does not stop the prompt even after confirming the credentials work in OWA
4. Confirmed he was not manually mapping the mailboxes in the Outlook profile configuration
5. Ran an online repair of his office suite.
6. Created a test user account and assigned full control to one of the mailboxes giving him the prompt for credentials and I experience the same behavior.
7. Toggled full access permissions off and back on
8. Disabled and reenabled inheritable permissions in AD
9. The user that reported the problem also has a Surface Pro with Outlook 2013 and he does not get the credential prompts on the Surface.
10. Even though the prompts occur and continually occur he is able to access the mailboxes and see new emails.
Any assistance is much appreciated.