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

I think the issue is a little more nuanced than Microsoft dropping the support of LSUB and not telling anyone + it wouldn't be on some mailboxes and not others. As you might recall, I have a test script Microsoft sent to me. After I'd done my initial testing and reported back to them, I added the IMAP command CAPABILITY to their script which asks the server to report back what IMAP standard it is working to. The results from my test are below:

Affected mailbox:

2022-11-23T16:49:40.4595128+00:00 C 0002 capability

2022-11-23T16:49:40.4887962+00:00 S * CAPABILITY IMAP4 IMAP4rev1 AUTH=PLAIN AUTH=XOAUTH2 SASL-IR UIDPLUS MOVE ID UNSELECT CLIENTACCESSRULES CLIENTNETWORKPRESENCELOCATION BACKENDAUTHENTICATE CHILDREN IDLE NAMESPACE LITERAL+

0002 OK CAPABILITY completed.

Unaffected mailbox:

2022-11-23T16:56:22.8614932+00:00 C 0002 capability

2022-11-23T16:56:22.8885873+00:00 S * CAPABILITY IMAP4 IMAP4rev1 AUTH=PLAIN AUTH=XOAUTH2 SASL-IR UIDPLUS MOVE ID UNSELECT CLIENTACCESSRULES CLIENTNETWORKPRESENCELOCATION BACKENDAUTHENTICATE CHILDREN IDLE NAMESPACE LITERAL+

0002 OK CAPABILITY completed.

You will see that the server reports exactly the same on both mailboxes - IMAP4 Rev1 - and that standard includes the LSUB command.

The Vivaldi folks obviously hit the same issue with their MUA as everyone else and I see in one of those replies that they noticed Microsoft's servers were reporting Rev1 too. I assume what they have done is engineered the problem out altogether by issuing a new build compliant with Rev2 which doesn't use the LSUB command anymore as it is obsolete in that standard. Nothing wrong with that approach, and other MUA developers could do the same with their products - accepting that they are being forced into unplanned code changes with limited testing, and that carries its own challenges and risks.

For those that missed it....

DISABLE the Thunderbird option: "SHOW ONLY SUBSCRIBED FOLDERS"

Located at: 'Tools' > 'Account Settings' > 'Server Settings' > 'Advanced' > "show only subscribed folders"

Uncheck that and then get messages and all folders will show up.

Having all folders shown is better than missing the important ones.

This provides at best an ugly hack to the problem that the last update (?) of Microsoft's MAPI (or OAuth2) implementation created in the first place.

However, this hack of changing the synchronization/subscription settings appears to work only for the Thunderbird mail client.

Be aware that a plethora of MUAs besides Thunderbird are affected. According to the other replies it has become apparent that such a solution does not exist for every email client out there.

And switching to Outlook is simply not a solution when affected users are on macOS/iOS or GNU/Linux - based operating systems.

The IMAP protocol - a de facto standard - should be adhered to, also by *Microsoft'*s implementation thereof.

Edit: It appears that the guys on the Vivaldi mail client development team have located the issue.

To my understanding Microsoft O365's IMAP implementation has dropped support for 'LSUB' without documenting this.

See their discussion: https://forum.vivaldi.net/topic/80723/lsub-failed-with-office-365-imap-server/9

For those that missed it....

DISABLE the Thunderbird option: "SHOW ONLY SUBSCRIBED FOLDERS"

Located at: 'Tools' > 'Account Settings' > 'Server Settings' > 'Advanced' > "show only subscribed folders"

Uncheck that and then get messages and all folders will show up.

Having all folders shown is better than missing the important ones.

Dear Michael,

 

Good day!

Thank you for posting to Microsoft Community. We are happy to help you.

 

Based on your description, I understand that you have a concern with "Unable to subscribe to Office 365 IMAP folders from MUA" At this very moment, I am looking into whether there could be a possible solution to this issue. I will get back to you as soon as I get any additional information about your query.

 

Your patience and cooperation are much appreciated.

 

Sincerely,

Ashraf | Microsoft Community Moderator

Any progress from your side Ashraf?

I simply cannot believe it. One month since the initial bug report and no fix yet; shouldn't this be a high priority issue?

The bug hit me just yesterday. Our university had the grandiose idea to switch their email server from a local one to the Microsoft 365 cloud.

Looking at the number of people that are using Linux, or macOS-based operating systems, I'd image that thousands of users are affected by this broken implementation on our campus alone. And we even paid for that mess with taxpayer's money.

You would assume that these things are being tested before they are being deployed on a large scale?! Well done Microsoft, well done...

I chased it up on the 30th and no update - and I did point out that they had been sat on a service affecting fault for a whole month.

My previous advice still stands. Each individual O365 system administrator with affected users needs to be raising their own service request in Admin Centre - and perhaps cross referring to the one I have already posted up if they are certain they are seeing the exact same fault. It only takes a few seconds to do this from the O365 Admin Centre menu (see below) so there is no excuse not to, if people want to see this fixed.

Imagining that thousands* of users are affected is not the same as Microsoft having it evidenced to them in the form of incident reports.

*You may well be right, but remember that this is far less likely to affect corporates who will tend to own and be in complete control of end users devices, and will generally be on Outlook over MAPI - so this will simply not be on Microsoft's radar as a priority unless those of us who are affected put it there.

My O365 tenant is non-profit related where I have no control whatsoever over the email client apps my users choose to use, and educational establishments will tend to be in a similar position with their students.