That option would actually be to leave a copy on the server. It is offered only with POP-connected accounts, because by default POP moves messages from server to client, i.e. it downloads to the client and then removes from the server. You can elect to leave a copy until you delete it in the email client. I have never quite worked out how that works, particularly if you move a message after downloading it.

By its nature, IMAP leaves all messages on the server. If you don't want to leave messages on the server, set the account up again using POP.

If you want or need to use IMAP, then the way to "download" messages from the server and then delete them from the server is to move the messages to the Local Folders account in Thunderbird.

Mailwasher, by its design, leaves copies on the server. Its role is to provide a safe place where you can examine messages and zap the nasty ones before running your email client. So it has to be able to show you what is on the server but not delete everything.

I tried moving all Inbox messages to Local Folder "2Inbox", but they still show up on my phone. I am used to POP, & I want the messages to vanish from my phone after I read them on the PC.

I thought the above solution would do this, but after moving everything to Local Folders, the same messages are still on my phone... A new message just showed up, so the phone should have shown only that new message.

I would rather not go back to POP3, since every time I reinstall TBird there is some hassle.

Any ideas for a fix?