1. Are you using an IMAP mail account?
2. What mail provider provides the mail account?
3. What is you IMAP mail providers retention policy on mail in the trash?

Thanks for replying, Matt!

IMAP is gmail.

I can't seem to find the info on gmail's retention policy, but once it's been downloaded to my Thunderbird and then transferred to the Trash folder, shouldn't it just stay there? Things in the In box do stay there -- it's only the Trash that is getting emptied. I've got messages in the In box going back more than a year, but every day messages older than one month drop out of the Trash folder.

reading here https://support.google.com/mail/answer/7401?hl=en&co=GENIE.Platform%3DDesktop It read to me like Google remove the trash folders content after 30 days. That is consistent with your observed reality of a month.

This seems to be about how to handle your mail through a Gmail app on your computer. I'm not using a Gmail app -- I'm using Thunderbird. Is there a setting in Thunderbird that says how long messages remain in the Trash? I just want to repeat the clue that they used to stay there forever.

Thanks!

Back again with more info -- an exchange with the Gmail forum:

'My question: But has [30 days for messages before Trash is emptied] always been the Gmail policy?

Answer: Yes, since day-one, for both Trash and Spam. But that doesn't mean that Thunderbird's Trash is linked to or connected to Gmail's Trash. If they ARE linked, then it makes sense that when Google deletes messages that would sync to Thunderbird.'

Any ideas?

Is there a setting in Thunderbird for how long messages are kept in the Thunderbird Trash folder?

Hello,

Try changing settings at:

Tools > Account Settings > Server Settings > Server Settings > When I delete a message:

and/or

Tools > Account Settings > Synchronization & Storage > Message Synchronizing and Disk Space

I don't know if my settings shown in screenshots will work for you but try changing.

Art

Back again with more info -- an exchange with the Gmail forum: 'My question: But has [30 days for messages before Trash is emptied] always been the Gmail policy? Answer: Yes, since day-one, for both Trash and Spam. But that doesn't mean that Thunderbird's Trash is linked to or connected to Gmail's Trash. If they ARE linked, then it makes sense that when Google deletes messages that would sync to Thunderbird.' Any ideas? Is there a setting in Thunderbird for how long messages are kept in the Thunderbird Trash folder?

No there is not a way to override the gmail retention policy. The trash folder is identified and set as a part of the IMAP connections process and whatever is the gmail policy for retention will be reflected in Thunderbird.

You can set thunderbird to move deleted mail to another folder, but Gmail will not act on it as if it is trash, and you will effectively have two folders identified as trash folders in Thunderbird for the account. That is about the best you can do.

Personally I would stop deleting things you need.