Reply-by-email: "pop3 polling delete from server" checked, but Gmail keeps messages anyway

Checked since the forum is open and configured:


I checked the inbox content, the forum content, and the messages are correctly published on the forum.

However, the messages aren’t removed from the inbox:

Any idea why?

Note: I just checked log mail processing failures to see if it can be of any help for future messages replied by email. It was unchecked by default.

Should I set this option as well?

Sorry it’s in French, but the option says:
When messages are retrieved by POP protocol: “delete the original copy from Gmail”

re-edit (I’m an edit specialist…):
On my other two forums, both Gmail accounts have this option set to “Archive Gmail’s copy” and, indeed, all the reply-by-email emails are archived in the Gmail account. I never paid attention!

So, two questions:

  1. Can you, sort of, “double confirm” that I need to set this option to “delete Gmail’s copy”?
  2. Why “pop3 polling delete from server” option doesn’t work? Is that because of Gmail’s specificities, and the option would work for other email providers?