Shared Mailboxes or Calendars not updating since mid Jan 2022 unless disable Shared Mailbox Caching

Copper Contributor


We're an MSP and since around 17th/18th Jan we've had one or two users in 7 different companies (tenants)  report issues with shared mailboxes or shared calendars they have access to not updating.


We've been able to get working again by simply unticking option in Outlook profile to cache shared mailboxes. 


But with this amount of clients with the same issue, I've not been able to see anything regarding known M365 health / windows update issue that causes this in the last few days.  Anyone else seen this issue and know root cause or have any acknowledgement of known issue 

52 Replies

@gblackburn came here because we are having the same issue with multiple users. I will try your fix but this bug needs to be worked out. 

Have multiple users in my organization with this same issue. Latest Office 365 Update may be the culprit? We are on Current Channel for updates and the latest update came out right about when this issue started.

@gblackburn  My company is having the same issue, since we don't install the account in account settings there is no way to cache the inbox.  Anyone find a fix for this yet?

I've picked up the same issue 19/01/2022 with multiple users using various shared mailboxes.  Any advise would be helpful


We have the same issue on multiple users and multiple shared mailboxes, since Jan 10 2022

@MicheleRJ tried the shared mailbox cache off and it worked for 10 min and then same thing again

@gblackburn same issues here. Hopefully there will be a solutions soon.

Same issue here, since last Office update.It seems like a bug.
We started to have this issue too. It appears to be escalating throughout our user base.

@gblackburn I've seen the same thing with multiple users. First report was January 20th. 

Same issue here. All I want to do is sync my calendar with another calendar account. But while it syncs when I initially add the calendar, it will not pull through any updates made after the initial add. So frustrating. It's forcing our team to utilise an alternative shared calendar solution in the meantime.
@gblackburn - our law firm is having the same issues, started around Jan 11. We have multiple users accessing a user account. Started having issues with employees unable to search and new items not appearing in the inbox. Have unchecked the "download shared folders" cache for most users and it was ok for awhile, but now we are seeing everything from deleted emails reappearing in the inbox, to draft emails disappearing, to the inability to change a category on an email and have it stick, and searching remains an issue. Not all users are experiencing the same problems, but almost all of our users are experiencing some issue. This shared mailbox is our incoming email box for all of our workflow and this is causing major efficiency issues for the users and myself having to try to troubleshoot the problem. It is too coincidental for everyone to have the same problem at the same time. Had to be something in the recent update. Help please Microsoft.
Exactly the same problem here, seems to be getting worse and spreads out through my organization

I managed to fix the problem by manually going to the few people who had the issue, removed the "Download shared folders" tick under Advanced in Account management, close Outlook and open it up again.  Then going back intro the same settings and switch it back on again.  This will start a sync of the Shared mailbox back to the OST file and update automatically again.  Hope this helps until we know why this started happening.



@EmileSteenkamp This was my workaround when I posted the question but you have made in clear for anyone who comes here.
As of 19/1 (but I did not see visibility of this till 22/1) it looks like this has now appeared in the public domain as an M365 issue. So we await a Microsoft fix with another suggested workaround below:

January 21, 2022 11:16 PM
Title: A small percentage of users' shared mailboxes aren't automatically refreshing new email in the Outlook desktop client

User Impact: Users' shared mailboxes aren't automatically refreshing for new email in the Outlook desktop client.

More info: While we're focused on remediation, users that have access to Outlook on the web can use this connection method to bypass this problem. Some affected users have reported that manually refreshing their folders using key shortcuts, such as pressing F9 or CTRL + M, may result in intermittent success as well.

Current status: We're continuing to review Fiddler trace logs and are in the process of gathering additional Time Travel Debugging (TTD) traces from our internal reproduction of the issue to provide insight into the cause of this problem and identify possible mitigation options.

Scope of impact: A small percentage of users aren’t seeing their shared mailboxes automatically refresh.
@gblackburn, Yes I've found that by only unticking the "Download Shared folder" it worked, but users were complaining about very slow response, so by ticking it again, it started to work. If you select the Inbox of the shared folder and click on "Update folder" that also works, but who wants to do that 100 times a day.
Started experiencing this about a week and a half ago. That it was just a fluke but it is definitely a lot more widespread. Had to resolve it for about half a dozen users using the unticking/reticking. So far that fix is holding up, so crossing my fingers. It is not just some coincidence. Either a recent Office update caused this or something on the backend. Hopefully Microsoft can issue a patch like they did for the VPN issue we saw recently.

Experiencing the same behavior since mid Jan indeed. Seems clearly a bug, as it's getting more widespread. Unchecking 'use cached mode' fixes it, but that's not a real solution.

@gblackburn  We're having the same issue too accross lots of mailboxes, we do not have the IT resource to go around and manually rebuild all the profiles, or change the cached mode, we need an urgent fix!