Anyway, The fact that there is a setting in Account Settings -> Synchronization & Storage -> Do not delete any messages and TB still deletes the trash it its own discretion sucks.

Generally I see this same sort of opinion and misunderstanding frequently from folk with IMAP accounts. If you choose to set up a POP mail account, all data is stored on your local machine and that is considered to be the canonical reference for mail.

If you have chosen to set up an IMAP account then the server copy is considered to be canonical. That is how the IMAP standard is setup. There is nothing an IMAP compliant mail application can do but honor that standard. SO if a mail is removed by the server, either through some sort of aging deletion, or because it was deleted in another instance like a phone or tablet, Thunderbird must dutifully synchronize the folder content to the canonical source. The mail server. This is why you see mail being deleted, because the server no longer has that mail in that folder. It is that simply.

Reference IMAP standard https://www.rfc-editor.org/rfc/rfc9051 POP standard https://www.rfc-editor.org/rfc/rfc1939

Thank you for your reply

Although I understand your point about IMAP and it synchronizing the mailbox. I am talking about the fact that Thunderbird deletes aging emails, or has a process of removing emails from the deleted items. I would prefer a setting that would stop thunderbird from doing this.

So if there is "some sort of aging deletion" it would be nice to have a setting to disable this

What Matt was saying is that Thunderbird can't protect anything from being deleted from a folder that is synchronized with a mail-server folder. If the mail-server (e.g., GMail) has a policy that any mail in Trash gets deleted after it has been there for 30+ days, Thunderbird cannot prevent the disappearance of old mail from your synchronized Thunderbird Trash folder. If the mail is gone from the GMail Trash folder, it's gone from the Thunderbird Trash folder.

However, Thunderbird has Local Folders, and your IMAP mail-server can't touch those. They are strictly local, on your computer. You can create local folders and you can store mail in local folders as you wish, and your mail-server will not manipulate the contents of those folders.

If you have items in your IMAP account Trash folder that you do not want GMail (or your mail-server) to delete, select those items in the main Trash folder, right-click, and choose Move To, and follow the arrows until you get to the local folder where you wish to store those items permanently. Thunderbird will not delete any of those items, and your mail-server cannot access them. But if you have moved an item from the account Trash to a folder in your Local Folders, do not waste time looking for that item online in the Web interface for your mail-server. It won't be there.

Attached is my layout of folders. I use the Local folders for local storage, and I monitor those folders to make sure they don't grow too large.

Thanks for your reply. I do understand this synchronization process. I think I did not initially provide enough context.

I am using Dovecot for IMAP, there are no external devices or software that auto delete my stuff from the trash and Dovecot has nothing that delete from trash that I know of. This apparently, after reading this thread [https://support.mozilla.org/bm/questi.../1362804|here] really is ThunderBird deleting from trash.

So this is why I posted this, to know how I can comment about this policy and that there should be an option to stop this from happening.

So far as I know, the available option is to move anything you don't want EVER to be deleted by Thunderbird OR your mail server into Local Folders on your machine. Thunderbird provides a convenient place for you to use already available folders under Local Folders or to create new folders under Local Folders. Again, so far as I know, things in your Local Folders folders are untouchable when the "deletion monster" comes calling.

Thanks for your reply. I do understand this synchronization process.

No I do not think you do, other wise this discussion would have ended days ago.

I think I did not initially provide enough context.

Probably not as I had to take a guess what email protocol you are using.

I am using Dovecot for IMAP, there are no external devices or software that auto delete my stuff from the trash and Dovecot has nothing that delete from trash that I know of.

Try a quick google of doveadm expunge -A Perhaps look at this 2011 discussion. https://serverfault.com/questions/254588/emptying-trash-with-dovecot-imap Things have possibly changed to make it simpler for server admins, as I have never managed a dovecote installation I really am not able to comment on the functionality that is invoked, but it is this concept you appear to be having difficulty with. The server cleaning house all by itself (or at least as far as you can see)

This apparently, after reading this thread [https://support.mozilla.org/bm/questi.../1362804|here] really is ThunderBird deleting from trash.

I really do not understand how you can extract that understanding from a discussion about BT IMAP servers emptying the trash if the mail is over 30days old and Thunderbired syncronising that change locally.

So this is why I posted this, to know how I can comment about this policy and that there should be an option to stop this from happening.

Sure you can stop it, have the Dovecote admin change the way their server ages mail and empties the trash so it meets your expectations. Based on your statements, this is in no way related to Thunderbird.