Outlook on Mac - Shared mailbox becomes no longer available.

New Contributor

I recently needed to wipe M365 from my Macbook and setup from scratch.

On setting up Outlook, realised they had implemented the ability to add shared mailboxes, just thru the main logged in user, via delegated permissions. Happy days. My previous setup, created a few years back, had the shared mailboxes added as regular mailboxes but as I say, all that setup has now changed.


I've got 3 shared mailboxes I added and all worked fine. One of them however (for support@) keeps coming up saying "This shared mailbox is no longer available". It doesn't receive new emails, etc and is in limbo. Closing Outlook and opening again gets it working, for a while buy the not available comes back after variable times; sometimes few minutes up to days. Other 2 shared mailboxes, I have included, work fine.

I'm using Outlook for Mac, Version 16.74 (23050300), the latest at this point. It was happening with the last couple of versions too.


Anyone else having this?

Any ideas how to resolve or diagnose?



Alan Wright.


4 Replies

We are also experiencing this on one of our Macs. So far no resolution. We've tried everything except a system reset. @wrighta16 

@wrighta16 would be interested to know if you found a solution for this? Having the same issue after trying the 'New Outlook'. Lagacy version still has the same problem now

I worked round the problem by removing the additional mailbox as a shared mailbox then added as a separate account. I always edit the credentials of my shared mailboxes much the same as a regular user account, so used these to add it as a new account. It’s worked ever since just fine. It shows slightly differently in the left-hand panel vs shared mailboxes but otherwise just fine. I used to work this way for all shared mailboxes I have before they added the ability to have as shared ones but seems there are issues with this.
Hope that helps. Please let us know if that also works for you too.


We are having the same trouble with 1 shared mailbox which is configured on different systems.

3 Mac's (MacOS 13.4, 13.3.1 and 11.7.7) have these problems of being unavailable after a certain amount of time.

1 Mac the same shared mailbox is working just fine. (MacOS 13.4)

All Macs have the latest Office (16.73)


No clue how to solve this.

So hoping someone has a solution.