Do you have access to a webmail interface with your email account? Do they show up there?

Might you have one of the Quick Filters engaged? If those buttons are hidden you can reveal them with the menu option View | Toolbars | Quick Filter Bar.

It's possible the folder index is corrupt. You can repair it by right-clicking the folder name, choose Properties, then Repair Folder.

Yes, I can check and see the huge amount of trash via webmail. On webmail I see: " Messages that have been in trash and spam more than 30 days will be automatically deleted." However that is not being done!

I played around with the quick filters and nothing changed. (Well actually now when I do a search a new tab in thunderbird opens--annoying!) I use quick filters to find a specific email, but that's about it.

I already tried the "Repair Folder" suggestion which was given in response to a previous inquiry. Nothing seemed to happen. Certainly it didn't make the messages appear.

Thanks for the suggestions.

Check this filter: select the 'Trash' folder 'View' > 'Threads' > 'All' should be selected.

Maybe you have accidentially set some threads as 'ignored' which I've known to done by mistake when people have selected an email and then press the K key. so in addition select 'View' > 'Threads' > 'Ignored Threads' Do you now see more threads which have a small red circle in the threads column?

Info on ignored threads:

• https://support.mozilla.org/en-US/kb/ignore-threads

re :I played around with the quick filters and nothing changed. (Well actually now when I do a search a new tab in thunderbird opens--annoying!)

Heads up info on this issue.... When you type in the Quick Filter search it starts looking for potential matches immediately based on your input - you do not need to press the 'Enter/Return' key - some people do this by default because they have developed a habit of auto pressing that key. If you press that key, it is the quick shortcut option to force the Quick Filter to become a Global filter without the need to retype everything in the Global Search.

re : On webmail I see: " Messages that have been in trash and spam more than 30 days will be automatically deleted." However that is not being done!

Are you on a paid Proton Mail Plan ? If no then the auto function would not work.

Are you still using Proton Mail ? Located this info on proton mail website https://proton.me/support/auto-delete-unwanted-messages

I did notice the following which may or may not apply - only you can check it: If you receive an email with an expiration date set by another Proton user and move it to your trash or spam folder, the message will retain its original expiration date. It will be automatically deleted on the date set by the sender. If the webmail account is not behaving as expected then that is an issue you must take up with Proton Mail.

re :I played around with the quick filters and nothing changed.

In the Quick Filter: You would need to ensure nothing was highlighted/selected - that means eg: if the Pin icon was selected then it might be applying a search criteria you had used in a nother folder. Also check nothing was in the search. Then you would know the Quick Filter had no filters effecting the view.

Quick Filter is All Clear. If I use the Quick filter to search while in the trash folder, it opens and switches to a new tab with an unfamiliar format (which I do not like) and includes mail that has deleted long ago. I am looking at one that was brought up from 2014! It is unreadable/encrypted, but there it is. Yikes! However if I Quick filter in a folder for recent mails that have not been deleted then it works as I am used to. Would any of this have to do with the demise of Windows 10 which is what I am using? ( I just ordered a new windows 11 loaded computer since mine can't be updated.) I don't want to think so...it's supposed to be good until October!

I suggest that, just to get past this situation, that you do your houskeeping task on the webmail interface: delete most or all the messages you know you don't want. Once you get the number of messages down to a more reasonable level, create a new temporary folder and move the remaining trash messages there so you have an empty Trash folder. Then, on local Thunderbird, see what Thunderbird shows, just out of curiousity - is it accurate now? - then right right-click on the folder and choose "Empty Trash".

Another thing to check... look at Tools | Account Settings | <the account in question> | Server Settings. What does it say for "When I delete a message:"? If "Move to this folder", you might click on the drop-down list and confirm that it's pointing to a valid, correct folder.

Also while in that area, check ...| Syncronization & Storage | Disk Space | To recover disk space, old messages can be deleted, both local copies and originals on the remote server." What is it set for?

re :If I use the Quick filter to search while in the trash folder, it opens and switches to a new tab with an unfamiliar format (which I do not like) and includes mail that has deleted long ago.

As I said - when using Quick Filter search on any folder - only enter text in search - do not then click on the 'Enter/Return' key because pressing that key means stop the Quick Filter and do a Global Search using same criteria which opens in a new tab. That Global Search will now search on all folders and if global search database is out of synch then it might show emails you have since deleted.

re :Would any of this have to do with the demise of Windows 10 which is what I am using? No.

So, I created a temp trash box, moved a few days' worth and then deleted the rest via my webmail access. The result was that the count via Thunderbird did clear. Then I deleted some emails today as I read and finished with them. Trashed emails showed up when I took a look to check, but then after going back to the inbox and once again checking on the trash...nothing is displaying. The count seems correct--about 100 instead of over 1000.

Thank you, Lin and Toad-Hall, by the way, for your constant attention and suggestions!

I am now cognizant of the Quick Filter message re: hitting "enter" to widen the search to "all folders."

I had to get a new computer because of the fate of Windows 10. When I put Thunderbird, the bridge and Proton mail on this new device--yahoo! All I have to do now is get all my contacts moved over...it's been tedious.