Thunderbird no longer removes emails once I clear them from the server

Is TB Android using imap or pop to connect to the server?

Can you check the following setting has not been disabled. Settings > account name > fetching mail > Sync Server Deletions

This is applicable only for imap. Pop doesn't support synchronisation.

It's Pop3. It all started after the last update a couple of days ago. Nothing was changed on my end.

The last update (v23.1) had only a single change that would not cause the behaviour you observe.

• Fixed: Attachment filenames with non-ASCII characters were incorrectly decoded and saved

For pop connections, it's the expected behaviour for emails to remain on your phone after they've been deleted from the server. Pop doesn't support synchronisation.

You can read more about the two protocols here.

I need Thunderbird on Android to start removing them again once I clear the server.

To achieve this, you would need to use an Imap connection in the mobile app.

This keeps emails on your phone synchronised with the server. When an email is deleted on the server, it will be removed from your phone.

Actually, just the opposite. Pop3 removes them from my app once they are removed from the server. It has been happening for 30+ years, and it stopped yesterday. This has happened once before and it WAS a setting changed that Thunderbird made. So, it always clears the app once I remove from the server. Thunderbird did an update yesterday, that feature stopped working yesterday? Come on Thunderbird, dig a little deeper please?

Come on Thunderbird, dig a little deeper please?

This is a community forum with the majority of responses coming from users just like yourself trying to help others. Please be respectful.

I realize what this forum is. There was nothing disrespectful with that comment. Just thought maybe Thunderbird people troll here every once in a while.

Besides, who are you to tell me anything when I have an issue, and somebody who doesn't know what they are talking about tries to tell me what the issue is, and it has nothing to do with my issue.

I have since created a mock POP3 test server using Python and verified the behaviour myself.

The setting I highlighted in my initial reply is indeed the relevant one. Enabling it causes local messages to be removed when they have been deleted from the server. It applies to both IMAP and POP accounts:

Settings > [account name] > Fetching Mail > Sync Server Deletions

My mistake was assuming that Thunderbird followed the more conventional POP3 model, and therefore that this setting would apply only to IMAP. That assumption was incorrect.

This divergence is noted in the following Thunderbird for Android issue:

K-9 Mail never supported POP3's "download then delete from server" model. The app tries to treat POP3 accounts similar to IMAP where we download copies of messages but treat the server as single source of truth.

https://github.com/thunderbird/thunderbird-android/issues/4974

It is worth adding an important clarification here. The wording in that issue could give the impression that POP support is going to be removed from Thunderbird. That is not currently the case: Thunderbird has stated that there are no plans to remove POP support. This clarification is not stated in the issue above, but is addressed by a Thunderbird maintainer in issue #9094:

https://github.com/thunderbird/thunderbird-android/issues/9094#issuecomment-2842184393

I'm perfectly happy to acknowledge when I've got something wrong, and in this case I was wrong about how this setting applies. I apologise for that.

I have also tested version 23.0 with Sync Server Deletions enabled, and then upgraded to 23.1. The setting remained enabled after the upgrade, so I could not reproduce the setting being disabled as part of that upgrade.

That said, I think there is an important distinction between disagreeing with a suggestion and dismissing the person making it. If a proposed solution doesn't apply to your particular situation, that's entirely fine, and simply explaining why it doesn't apply provides useful information.

Troubleshooting is fundamentally a process of elimination and information gathering. Not every issue is resolved by the first suggestion, and suggestions that turn out not to be the cause are still part of that process.

People volunteering their time to help are not under any obligation to investigate an issue further, so I think it is reasonable to disagree with suggestions while still acknowledging the effort made to provide them.

If suggestions about possible causes aren't wanted, it's difficult to see what purpose asking for troubleshooting assistance serves.