How about right click the folder and select empty trash.

You might want to right click and select properties then the repair button as it sounds like either the trash folder or it's index is corrupt (1/1/70 dates) Repair will fix the index, but a compact will be needed to fix the actual folder data.

Note that a common cause of such things are system activities that interrupt the file access and write. Things like antivirus scanning, cloud syncing of the location, slow network responses when the data is on a local server or NAS or some form of streaming backup is in use.

Thanks for the reply. I don't want to delete all the trash. I want to keep the last few months. Is that possible?

Are you talking about a gmail pop account?

It is quite normal for many servers to auto empty the server Trash folder periodically and that can range from a few days to a month. But this would only effect people using Imap mail accounts.

If you are using a gmail pop account, it could mean you are not deleting emails off the server if emails are not put into the server Trash folder. Advise is to periodically logon to webmail account and check to see if really old emails need to deleted in order to increase the amount of quota you have on server.

How to delete messages in Trash that are eg: older than 30 days.

• Right click on Trash folder and select 'Properties'
• Select the 'Retention Policy' tab
• Uncheck the checkbox 'Use my account settings'
• Select 'Delete messages older than' and choose the number of days eg: 30
• click on 'OK'

The problem was not with gmail. Regrettably the problem has fixed itself when I accidentally deleted the trash in Thunderbird. Not a catastrophic issue as all the deleted emails are still in Gmail

Always the same issue since more than 10 years !

After deleting many e-mails reappear in "unified folders" with the date 01/01/1970...

Always the same issue since more than 10 years ! After deleting many e-mails reappear in "unified folders" with the date 01/01/1970...

Have you considered asking your own question if the information here does not fix it for you?

But my guess is your current issue and this topic you posted in 2022 https://support.mozilla.org/en-US/questions/1382907 are identical as is https://support.mozilla.org/en-US/questions/1386315

Regardless of your opinion the response you received in that topic was unacceptable, it is probably the best you will get until you stop your antivirus from causing the issue in the first place, either by creating an exception that prevents it scanning in the Thunderbird profile folder while the program is running and accessing files, or removing it entirely and using Microsoft Defender. Your index is being updated with corrupt information and the primary cause of that is the antivirus.

Other less frequent causes are;

• Not allowing time for your changes to an IMAP account to synchronize properly (10minutes of so for larger numbers of changed mails) before the application or system is shut down.
• Having the Thunderbird profile folder located in a part of the drive that is syncronised to the cloud or a streaming backup.
• Having the Thunderbird profile located on a NAS device of a saturated network connection.
• A potentially failing drive with bad sectors on it.

This is a very individual specific topic with a couple of generic common causes at the top of the list and some very technical ones as they get rarer as a cause of the failure.

Sounds like your file is corrupted.

How frequently do you compact folders? After deleting several emails you chould be compacting folder to remove all old traces and this helps to maintain a healthy file.

But all too frequently, Anti-Virus programs try to 'fix' files and mess them up because they do not understand the one file contains many emails.

Suggest resetting the virtual folders.

• First 'View ' > 'Folders' - select 'All' - uncheck 'Unified' to switch it off.

• Help > Troubleshooting information
• Under 'Application Basics' - half way - Profile folders - click on 'Open Folder'

A new window opens showing the contents of your profile folder.

• Exit Thunderbird now - this is important.

• Scroll down and delete this file: 'virtualFolders.dat'

• Click on 'Mail' folder'
• And delete this folder : 'smart mailboxes'

Start Thunderbird. Allow mail to get downloaded in all accounts. Then reselect the View to show 'Unified'