Unable to subscribe to Office 365 IMAP folders from MUA since 2022-11-01

All - my latest test findings as follows:

I took the decision today to run the diagnostic to temporarily re-enable IMAP/basic auth on my tenant (this gives system admins a bit of extra time if they were caught out by the basic auth deprecation), and see if the fault is still there with an affected account reconfigured back to basic auth.

Findings as follows:

1. It doesn't make the slightest bit of difference to the fault - an affected account remains broken for subscription. So this doesn't appear to have any connection with the basic auth change/setting. This is what I expected if I'm honest as the change hit my tenant early in Oct and this problem didn't appear until a few days back.
2. Because my tenant accepts basic auth now, I was able to add an affected account as type IMAP to Outlook 2021 on my test machine and that gives the Outlook error "The folder list was not fully refreshed. An IMAP command failed" when I tried to query IMAP folders. Ticking the equivalent box to TB to display all folders works in Outlook too. I then added one of my known working accounts to Outlook as IMAP, and subscription works fine on that.

So, what this proves in summary is the fault presents itself the same in both Outlook 2021 and Thunderbird and the fault is sticking rigidly to the affected accounts. So it rather looks like the problem is at the O365 end on a number of tenants.

I have updated the ticket I have open with Microsoft for the fault on my tenant.

I have three accounts as mentioned in my post above. One of the three still works. This working account is used only for testing and has had little use lately. The other two have a lot of activity. So my thought is that whatever algorithm was used to change the two not working was based upon usage and that sooner or later the 'test' account will stop working. I'm not much in tune with MS and got hit by the OAuth2 deadline. One of these accounts stopped working at 3:24 AM Oct. 6, and the other two within the next two days. If my memory is correct the 'test' account worked longer with basic authentication than the two that have a lot of activity. Anyway with so many experiencing this problem I agree that MS must have changed something. Maybe they will change it back or at least let developers such as TB know what has changed and what they need to do differently.

I'm having the exact same issue for accounts on my tenant. In my case, deleting an affected O365 account from TB and re-adding it resulted in the fault returning. I took that same account and added it to a separate test machine with a fresh install of TB on it, and got the same fault again.

Ergo - this fault is staying with the affected account(s), and not the device accessing it. The identical TB (Oauth2) config has been used throughout my testing as evidenced by the fact that I can send and receive quite happily on an affected account, and I can see the folders if I set TB to display all folders regardless of subscription.

What I did find is if I added some test accounts from my tenant that hadn't been accessed via IMAP before, that actually worked perfectly well including the subscription functionality. I now have three such accounts which have been working OK for several days now.

So it appears that something has happened that has broken JUST the IMAP subscription functionality, and on accounts that were using IMAP at the time the problem occurred.

Before anyone mentions deprecation of basic auth, the affected accounts were reconfigured to Oauth2 months ago in preparation for that change, and everything worked fine until the other day.

I have tried turning off IMAP on an affected account in Admin Centre, then turning it back on, and that had no effect.

I'm seeing the same issue. Thunderbird is reporting "SUBSCRIBE failed" every time I try to subscribe to any IMAP folder except INBOX.

I'm having the same issue with OAuth2 + IMAP as well. I've tried disabling/re-enabling IMAP on the mailbox and have double checked the app permissions in Azure AD. Hope this gets fixed soon.