Outlook on Mac - Shared mailbox becomes no longer available.

Brass 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.


11 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.




Hey Alan,


I'm having all the same issues as you. I find it confusing how it works for x amount of time (usually around 10 minutes for me) once I've readded the shared mailbox and then it goes back to showing the error message. It's hugely frustrating for me as I have over 10 shared mailboxes for work and having to use the web version currently.


Any tips / resolutions would be appreciated :) 



Hi @daniellebatt 


I already posted about how I worked around the issue. See above. 

Basically, don't use the flawed add shared mailbox option but use the add account and use the shared mailbox login credentials. I have a mix of both with the majority of shared mailboxes working as added shared mailboxes but just one that keeps dropping off. 

So it's the combination of that option and the particular mailbox...


Hope it works for you...

@wrighta16 I am using it now like adding the account with credentials. But now all coworkers have to this also. It was so simple by using the add mailbox. And it is sad Microsoft doesn't reply or fixing the issue at the moment.

Its also so weird that some shared boxes work like a charm and others don't.


Hope it will be fixed sone



I have fixed the same problem on my MacBook Pro running Ventura 13.4


After opening Microsoft Outlook then went to 'Tools', 'Accounts', selected the account that is linked to the shared mailboxes, clicked on 'Delegation and Sharing', clicked on 'Shared with me', then clicked on the '+' and added the shared mailboxes. Both are now working. it's been 30 minutes so far. fingers crossed.


The latest updates to both OS X and Microsoft seem to have cured the problem and you can now connect to your shared mailboxes in the correct way without having to create separate accounts (as per one of the suggestions above). I connect to 6 shared mailboxes and they have remained connected fror the last 48 hours. Hope it now works for you :)

I am having exactly the same issue i have added them but i cant see them in outlook...

If i try to add them again it says they have already been added but cant see them. fustrating. @wrighta16 

Maybe your profile prevent the shared accounts to apear. Make sure you use  the "All account" profile.