Authentication Failed when adding Shared Mailbox

Question

I work for the IT department and one of our users is having issues adding a shared mailbox to the Outlook app on their iPhone 12. They are able to add the shared mailbox in OWA and O365 desktop app without issues but when they try adding it in the mobile app, they receive the following message:

Authentication Failed

That didn't work. You may not have the right permissions to add this mailbox or this mailbox doesn't exist.

We have tried re-installing the app, updating from iOS 15 to iOS 16, and restarting the phone but nothing has worked. They were able to add shared mailboxes without issues. We have ensured the user has permission to access this mailbox and have confirmed this access by having them add the mailbox in OWA.

Outlook version: 4.2241.1

Answer 1

Dear LonzoAZ,

Good day! Thank you for posting to Microsoft Community. We are happy to help you.

Based on your description, I understand that you have a concern with 'Authentication Failed when adding Shared Mailbox'. Before we proceed, we need more detailed information about the situation you are experiencing.

Please help us in isolating the issue by considering the following information:

1. How many accounts does the user has in the Outlook on the iPhone?
2. Since it is working perfectly in Outlook client and outlook on the web, this might be the issue on the iPhone itself, have you checked to confirm he is using the account that is a member of this shared mailbox and has the "Full access" permission? If user have multiple accounts in Outlook Mobile, make sure to select the account that has permissions to access the shared mailbox. Add a shared mailbox to Outlook mobile (microsoft.com)
3. Have you tried the same shared mailbox with different account in the other outlook on mobile to check if it works fine there?

We look forward to hearing from you; Please understand that our initial reply may not always immediately resolve the issue. However, with your help and more detailed information, we can work together to find a solution. Thank you for your cooperation.

Sincerely,

De Paul | Microsoft Community Moderator

Answer 2

1. The user only has one account in Outlook on their iPhone.
2. I have confirmed the user is using the same account that is a member of this shared mailbox and has the same access as all other members.
3. Other members have been able to add the mailbox a while back without issue. I could have one of the other members remove the shared mailbox from their app and then try re-adding the mailbox, but it risks them running into the same issue and it is important they have this access.

Answer 3

We were able to resolve the issue.

The user once again re-installed the Outlook app from the App Store and when it asked them if they wanted to allow notifications, they accepted and then from there they were somehow able to add the shared mailbox.

However, they were unable to receive notifications for this shared mailbox and was only receiving them for their personal inbox. This was resolved by turning on calendar notifications for the shared mailbox.

Answer 4

Dear LonzoAZ,

Good Day!

I am glad to hear the issue is resolved after re-installing the Outlook app from the App Store and accepting the "if you want to allow notifications" prompt. Hope any other users with the same situation may try this to address his issue. If you need further assistance, feel free to post the issue in our forum. We are glad to help you.

Thank you once again for the generosity in sharing the solution to the community!

Sincerely,

De Paul | Microsoft Community Moderator

Answer 5

The way I was able to resolve this for my user was by having them connect to Wi-Fi and then try adding the Shared Mailbox. It did not work on mobile data. Once they were on Wi-Fi, the shared mailbox added without issue. So long as the user has access to the mailbox, this is generally a device specific issue which I have only seen with iPhones.

EDIT:

Other ways I have fixed this issue:

Reboot the device

Uninstall and reinstall Outlook and Intune

Have the user open/install the Microsoft authenticator (just need to open it)

Basically, this is a bug of some kind, and you just need to jiggle to proverbial handle.