log the connection and find out why it is re-fetching your headers. I think you will find it is the server declaring the folder out of date so it is syncronised.

Note log files get very big very quickly, so delete them often while you wait for an issue.

Matt

Thanks for your reply, and apologies for not updating this sooner.

Thunderbird is most likely synchronising folders - I access my mail on the sunscribed accounts on at least 3 different devices (home PC, laptop and Android phone using Bluemail), as well as direct web access to the accounts - after all, that's what IMAP is for. I will look at logging in case this shows any other issues, but it is most likely synchronising when this happens.

My question is why Thunderbird insists on expanding the whole folder tree whilst synchronising, which renders Thunderbird unusable during this process - a real pain if I need to acces mail quickly on the laptop during a meeting, for example. Additionally I then have to manually collapse all folders, which is time-consuming and frustrating. No other client that I use now (Outlook, emClient, email acces in Vivaldi browser) do this folder tree expansion - indeed, in Outlook it helpfully shows the Send/Receive process in detail and it carries on quite happily during the synchronisiation.

Thanks again for picking this up, Matt.

Can you confirm that the instructions at https://wiki.mozilla.org/MailNews:Logging are still valid for setting IMAP logging?

Thanks

Those instructions are still valid (I am the primary author).

All accounts that have this issue are specified as "download only headers"? How big is your gmail Inbox and other largest folder (number of messages)? And is it only the inbox that redownloads?

Thanks for the update

Maybe the "download only headers" is a clue. The worse affected one is a large, in term of folders and messages, account where I only download the headers due to limited local storage on the laptop - in fact this differs between the laptop where I download headers only and my main machine where I download the messages since I'm not short on space there. I'll try changing that and see what happens. There are probably over 100 folders with 1000 or more messages in all (I guess I could do a recursive count on the msf files to get the folder count - is there a way to get the message count?). I should split this up and maybe move old messages to a local folder, but if I do that then I would only have access to these historic mails from Thunderbird and, at this stage, I don't want to tie myself that closely to one client. I could set up another IMAP account on my own doman for old mails and not synchronise with Thunderbird which would probably help.

The issue is that the whole folder tree expands, including all nested folders even though the vast majority of folders will not have been changed - it's not only the folder tree leading to folders that might have to be resynchronised that open (I'm probably not explaining this very clearly - apologies).

I'll change the download options, get a count of the total number of folders (either brush up my Linux or knock up a Powershell script), set up logging and see what happens.

It's not expanding all my folders. But, you use Addons that can effect the Folder Pane.

Suggest you collapse several folders then restart Thunderbird in Troubleshoot mode.

• Help > Troubleshoot Mode
• Click on 'Restart'
• Click on 'Continue in Troubleshoot Mode'

Did all the folders get expanded again ?

Thank you for your continued help.

Before posting this I spent weeks - many of them - trying to get a repreatable way of provoking this action but failed to generate any pattern. It would behave sometimes for days on end, then suddenly expand the folder tree on startup. I always collapse the tree before restarting (oh for a collapse-all-folder-trees option)- sometimes a restart in troubleshoot mode would expand the tree again, sometimes it wouldn't. Same behaviour if not restarting in troubleshoot mode but a normal restart - sometimes a restart would expand the tree again, sometimes it wouldn't.

As you noticed (how, of ouf interest?) I have QuickFolders installed for convenience, but again this was happening before I installed that, and removing it still shows this random behaviour.

I have now uninstalled TBird, deleted the profiles in the AppDate tree, reinstalled TBird 115.8.1 and just set up my large account to simplify this as far as possible. Looking back at https://wiki.mozilla.org/MailNews:Logging in more detail I see a line

imap (not available in version 115)

so how would I set up IMAP logging, assuming this is what's needed?

As an aside I have had a career in IT and know how difficult it is to track down an intermittent issue such as this, so I don't neccessarily anticipate a quick fix, or even quickly isolating the problem. I'll see how this new install behaves and update this when there's something to report.

Thank you

With a minimal fresh installation I still have this issue of the folder tree being expanded when I open Thunderbird after completely collapsing the tree before exiting Thunderbird on the previous run, which I always do. It will certainly be synchronising on startup since I now use emClient for email since this makes Thunderbird unusable - no other client that I have used shows this behaviour.

As I asked in my last update, please will someone send me dtailed instructions on setting up the required logging since looking back at https://wiki.mozilla.org/MailNews:Logging#Thunderbird_Logging in more detail I see a line

imap (not available in version 115) - mailnews.imap.loglevel string, set to All, but only if you have set mailnews.imap.jsmodule=true for Beta and Daily channel builds only.

I don't think that I can make any progress without logging the behaviour now.

Thank you

I have this problem too! (for users that using IMAP and have more that 100 folders) and another one - TB are randomly messing up with msf files, which cause weird things, for example: New notification "There is new mail!", You will go to Inbox and hmmmm, I see no new mail, but there is (1) in Inbox folder. Only order to "repair folder" will bring back the new mail to the list.

So, I've googled back and forth for the solution, then I've found Betterbird (a Thunderbird fork that have applied bugfixes, that TB team are lazy to implement in current stream)

I've switched to Betterbird for testing purposes and bingo! https://www.betterbird.eu/#featuretable

PS: I'm not affiliated with Betterbird nor I'm shaming TB. I'm just tired to tilting at windmills of very annoying bug that are far cry abandoned (read: not fixed).

Many thanks Chris - Betterbird looks promising.

I bit the bullet and took out a Microsoft365 subscription since Thunderbird was becoming unusable so I'm now using the full-fat Outlook365 which, although having its own idiosyncrasies, is pretty robust and mostly does as it is told. The 1TB OneDrive is useful as well. Having a reliable Linux client will be very useful, though, and I'll give Betterbird a try.