Can't delete messages from Inbox by right-click > trash can icon; have to drag them manually to Trash

Yes the imap can keep pushing the email as it is kept on the server..

I use pop3 to download and keep on server for two weeks

That makes sense. IIUC, normally, if I put something in Trash in my desktop Thunderbird, the Webmail also grabs that email and stashes it in the online Trash... OK, just checked, and emails that I drag to the Trash folder in Thunderbird are also trashed by the server; but if I right-click and trash them in Thunderbird, the server doesn't trash them. I don't know why the two ways to do the same thing have different results!

Yes the imap can keep pushing the email as it is kept on the server..

You are wrong. Unlike a POP account, when you delete a message from an IMAP account it will NO longer be kept on the server >>>>> https://support.mozilla.org/en-US/kb/difference-between-imap-and-pop3 And even when you delete a message from your POP Inbox it will not be re-downloaded again because of the popstate.dat file.

I use IMAP to grab my mail, if that's important. the message disappears for a moment, then reappears. I can delete it by dragging it to the Trash folder in the folders pane on the left.

Go to Settings > General > Network & Disk Space > Disk Space and click on the "Clear Now" button

Alas, the Clear Now button hasn't helped!

Did you test running Thunderbird in 'Troubleshoot Mode'? https://support.mozilla.org/en-US/kb/troubleshoot-mode-thunderbird

Sadly, the same thing happens in Troubleshoot Mode...

Since this is an IMAP account you can easily delete it in Account Settings without loosing your messages. Nevertheless, for even higher security do NOT check ⬜ Remove message data (image) Then recreate the the same IMAP account and test deleting messages.

Still trying to fix this. Thunderbird is definitely re-downloading the messages I right-click delete. (I disconnected from the net, right-click trashed a message, which stayed gone until I reconnected, when it downloaded again.) Messages stay deleted if I drag them to the Trash.

Did you test deleting and recreating this IMAP account? I have never encountered this issue in TB forums and I have no solution. Does your Trash folder have the typical trash bin symbol ? Which action is checked in Account settings > Account name > Server Settings > "When I delete a message"?

Hi Mapenzi, thanks for your posts! I haven't summoned the courage to try deleting the account yet. To answer your questions, the Trash folder does have the normal trash can icon, and "When I delete a message" is set to send it to the Trash folder.

That makes sense. IIUC, normally, if I put something in Trash in my desktop Thunderbird, the Webmail also grabs that email and stashes it in the online Trash... OK, just checked, and emails that I drag to the Trash folder in Thunderbird are also trashed by the server; but if I right-click and trash them in Thunderbird, the server doesn't trash them. I don't know why the two ways to do the same thing have different results!

I would have said you found a bug, but I can not duplicate your experience using V153.1.1 in a Google IMAP account Or The daily build 157.0a1 Right clicking and selecting the trash icon moved mail to the trash folder (both tests done on a Gmail IMAP account on Windows 11 with defender as anti virus with the windows Firewall doing that job.

What does your environment look like? it appear to be windows 11 with a version of Thunderbird between the two I tested. What antivirus are you using?

Appreciate you Matt! I've got Malwarebytes 5.6.5 (x64). Should also mention I usually have NordVPN 8.3.10.0 running (turning it off doesn't fix my problem, however).