It sounds like you are using an imap mail account if you want to see folders on the server. You have to subscribe to see the folders. Right click on the mail account name in the Folder Pane and select 'Subscribe'. then check the folder and click on OK.

I already tried that and it did not make the folder reappear?? I also tried adding a new folder but no new folder appeared.

Are you saying that the 'Subscribe' window shows the 'missing' folder and it is already selected as 'Subscribed' or is the folder just not in the list so you cannot select it? Please clarify.

The Subscribe window does show the missing folder, which I have clicked on and subscribed to but the folder does still not show in TB. If I click to subscribe on my other email (gmail and hotmail) addresses all the folders are ticked as subscribed. Interestingly I have another @outlook.com email and right clicking on that one does not even give me the option to subscribe, yet all the folders are listed!!

There have been alot of similar cases with outlook/hotmail/office365 , so something is clearly going on.

Please try this to see if you can subscribe / show in folder pane again.

'tools' > 'Account Settings' > 'Server Settings' for the mail account or Right clickon mail account name in Fodler Pane and select 'Settings' select 'Server Settings' for the mail account click on 'Advanced' button uncheck: 'Show only subscribed folders'. clickon OK click on OK

then try to subscribe again. Right click on mail account and select 'Subscribe' See if this time you can select the folder. click on OK

tools' > 'Account Settings' > 'Server Settings' for the mail account or Right "click-on mail account name in Folder Pane and select 'Settings' select 'Server Settings' for the mail account click on 'Advanced' button un-check: 'Show only subscribed folders'. click-on OK click on OK The above appears to have worked and my folders are now displayed. However if I click on subscribe then none of the folders are actually ticked as being subscribed to. But looks like we don't need to go there as I have my folders back.

Many thanks Andrew

I've created a bug report, asking for this to be checked out.

• https://bugzilla.mozilla.org/show_bug.cgi?id=1241926

As this is not actually affecting me - I don't have outlook/hotmail/office365 mail account, then it would be helpful if you could offer information for the bugzilla people. Please tell them : what OS you use. what version of thunderbird. What server you are trying to connect to subscribe folders. state what folders disappeared. state whether you could see folders in the 'subscribe' window etc you would need to register/logon to post comment. It would also be usefult to 'Vote' for the bug. Voting is located in the top section where it says: Importance: (vote)

Further update to keep you in the picture. http://www.o365dash.com/

It would appear that Microsoft released a bad update to their office365 / outlook.com servers which broke IMAP folders. Microsoft are working on the issue and promise to remediate the situation. Whilst bugzilla will continue to monitor the situation, there is little anyone can do until Microsoft fix their problem.