The definition of the word expunge is 1. to delete or erase; blot out; obliterate 2. to wipe out or destroy

That pretty much explains it. When you delete or move mails from a folder (fx INBOX) the actual mails are still there within the folder-file but now marked for deletion. When you expunge or compact a folder it is rewritten to a new folder WITHOUT the deleted /moved mails The old folder is then deleted and the new is given the old name.

There is no way to reverse this. But for a mail to be expunged it has to be either deleted or moved. And you have to set it up in account-settings/server settings.

I didn't expunge the 2 emails. There was just a quick on screen message stating it.

I assume your account is IMAP. when emails are deleted in IMAP they are expunged from the server. So I would guess it is a note back saying the delete of your last two mail worked.

Expunge occurs at odd times. and almost always when Thunderbird compacts a folder.' What Thunderbird does with your mail when you delete it is mark it as such and hide it. Latter when things are slow it compacts the file and actually removes the mail from the file. That triggers an expunge event on the server for those emails. So those two emails might have been deleted by you weeks or even years ago. I am sure I have an account that possibly has never been expunged after many years because I has very very little mail go through it (I use it for testing) So were I to compact that account there would possible be mail expunged from 2012. An extreme case. But not all that much so.

Thank you.