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

Anonymous
2022-11-02T07:33:01+00:00

I'm using Thunderbird to access my Office 365 mail account and it has been working fine (a couple of month ago I also switched to OAuth2 due to deprecation of basic IMAP authentication). However, since 2022-11-01, Thunderbird is unable to subscribe to IMAP folders. Last time I know it was working was last Friday 2022-10-28. Thunderbird is able to list to available folders (e.g. when opening the "Subscribe" dialog from the mail account settings), but cannot subscribe to them. I enabled IMAP logging in Thunderbird, and it shows that the server answer the subscribe request with "BAD SUBSCRIBE".

It is not a password/authentication issue, as Thunderbird can still see the content of "Inbox" and "Deleted Items". And if I disable the option "Show only subscribed folders", it can access everything in my Office 265 account.

Edit: here's the relevant logs from Thunderbird (note: I've replaced the actual folder name with "xxxx"):

[Parent ...: IMAP]: I/IMAP ...:outlook.office365.com:A:SendData: 76 subscribe "INBOX/xxxx"

[Parent ...: IMAP]: I/IMAP ...:outlook.office365.com:A:CreateNewLineFromSocket: 76 BAD SUBSCRIBE failed.
Microsoft 365 and Office | Subscription, account, billing | For business | Other

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  1. Anonymous
    2022-12-06T19:12:31+00:00

    Thanks for keeping this going. I just got off a call with my support team and they are still thinking it is something on the client. I have to get my affected users to login on different hosts and reproduce the problem. I asked if LSUB is still the supported way to get subscribed folders and they will ask. They are not convinced it is something on the server yet.

    -Jonathan

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  2. Anonymous
    2022-12-05T19:35:22+00:00

    (the following paragraph is pure speculation from a user lacking the understanding of the actual communication protocol)

    Here a wild guess out of the blue: Perhaps we are running into path length issue? I recall the property of the Windows API to limit the MAX_PATH variable to 260 characters.

    Allow me to speculate: I assume that communication between user agent and server(s) depends on some kind of authentication token. It should also contain an (encrypted) account address or ID. Perhaps the list of subscribed IMAP folders is appended to account ID (or user email address) and token, and subsequently sent as part of the string in whatever server/client handshake. In this hypothetical setup, evaluation of the string on the server side may hit the size limit in some cases. This would occur in particular in cases where account names were too long?

    (back to the facts)

    I noticed that Ian's last email address is rather long. The name and password of my affected account are also on the longer end of the spectrum. Is there evidence suggesting a correlation between email-address, or password-length, and account behaviour?

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  3. Anonymous
    2022-12-05T18:25:37+00:00

    **************** EDITED DUE TO A TESTING ERROR ****************

    This and other feedback prompted me to do a bit more testing of my own this afternoon.

    I added a new account to my tenant today to see how that behaved. That account WORKS in both Thunderbird, and using the Microsoft testing script.

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  4. Anonymous
    2022-12-05T15:09:47+00:00

    I have three accounts on the same tenant subscribe works for one of them and fails on the other two. The one that works is a test account and is seldom used while the other two are active every day. I don't have admin rights thus have limited visibility to settings.

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  5. Anonymous
    2022-12-05T13:16:40+00:00

    Same here, at a Swiss University. Not all IMAP users are affected. Case opened @MS referencing ticket #33661676. Let's hope they fix this soon.

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