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

Thank you for mentioning the Thunderbird workaround!

I was contacted by Microsoft support who claimed that IMAP is no longer supported since Jan 1 2023. I cannot find any mention of it online, perhaps the representative was refering to IMAP Basic Auth being deprecated. https://techcommunity.microsoft.com/t5/exchange-team-blog/basic-authentication-deprecation-in-exchange-online-september/ba-p/3609437

Basic auth over IMAP was turned off in October (around the 3rd Oct on my tenant). But it was possible for system admins to re-enable basic auth for individual protocols on their tenants until a final deadline of the start of January - which is where Microsoft's incorrect/mis-leading reply probably stems from.

That is some first class technical support. The irony is that our orgs/companies are all happily paying for that support, so why would MS bother?

Thank you for mentioning the Thunderbird workaround!

I was contacted by Microsoft support who claimed that IMAP is no longer supported since Jan 1 2023. I cannot find any mention of it online, perhaps the representative was refering to IMAP Basic Auth being deprecated. https://techcommunity.microsoft.com/t5/exchange-team-blog/basic-authentication-deprecation-in-exchange-online-september/ba-p/3609437

First I want to thank everyone who has collaborated on pinning down this issue. This bug is stalling our organization's migration from G Suite to Office 365, since forcing every user onto the Outlook desktop app is not an option for us.

I have opened a support ticket with Microsoft pointing to this thread, requesting to be notified when the bug has been fixed.

1. Am I correct that there is currently no known work-around to this bug?
2. Is this bug acknowledged by MS and listed on some public bug tracker or similar where progress may be monitored?

From what we collectively know about the issue, it's highly unlikely it will affect "every user" you migrate. It will likely just be a small percentage of them - but there is no way of knowing in advance what percentage and which ones as we don't know what is actually causing it yet (and neither it seems, do Microsoft).

As David L says, there is a relatively simple (one tick-box) workaround for affected Thunderbird users, but if you plan to use some other IMAP mail client, you'd need to look at whether there is equivalent functionality in the settings of that product to override IMAP Subscription, which is the bit that is broken for affected users.

Hello! To your questions:

1. The fundamental 'workaround' is to use Outlook for the Web. No client but a browser is needed for that. If you must use an IMAP client, e.g. Thunderbird, then disabling the option that shows only subscribed folders is a workaround.
2. Yes, the bug is acknowledged by Microsoft, but not publicly, i.e. it has not yet been listed in the Service Status section of the Microsoft 365 Admin Center.