IMAP or POP3?

It's POP3.

I'd check your Earthlink settings as to how long you have told it to hold read emails before deleting them.

There is no such setting that I can find. Thunderbird was deleting emails automatically before, but for some reason it stopped. Maybe Earthlink changed something in Web Mail.

Well, there's nothing as strange as computers. maybe someone else has this experience.

I would change the TB setting, close TB, re-open and change the TB setting back. That sometimes works in a whole list of software. Also check that you haven't got the 'Until I delete them' button ticked.

"There is no such setting that I can find" - I'd be inclined to say that 'there's always a setting' for deletion of data. I'm not doubting you - but accounts are very keen to get data off their servers.

That worked (changing the settings, closing, launching, and changing the settings back). Thanks!

There is a delete setting in Web Mail for mail that is in the Trash folder. If there were a setting for deleting from the Inbox, I would expect it to be very close by the other setting. If there is such a setting, they did a very good job of hiding it because I have looked several times. And forget about trying to get support from Earthlink...