Status of email in the Mail Archive

If it is a Gmail account, that is Gmail's "All Mail" label. Mail maps it to the Archive mailbox.

It is populated by Goolag. They keep every email you have ever sent or received, even if you deleted it.

But I'm still wondering why emails I have sorted into 'On My Mac' folders either manually or via rules are still appearing within Archive/ All Mail...

Gmail isn't really IMAP. It slept in a Holiday Inn Express one night, but it still only pretends to be IMAP.

Gmail doesn't have folders or mailboxes. It uses Labels which are like Tags. A message can have many Labels.

A new message is delivered to your email client (Mail) with two Labels, "Inbox" and "All Mail."

When Mail moves a message, it removes the Label corresponding to the mailbox it was moved from, not any others. So, while the "Inbox" label was removed, the "All Mail" label remains intact, as Goolag wants it.

Goolag keeps all of your email in All Mail, even if you delete it. It makes it much easier to harvest your personal information.

On older Gmail accounts, you can turn off display of the All Mail label in IMAP clients. However, it appears that capability has been removed for new accounts.

I think you can still modify Gmail's settings to actually delete emails you delete and not keep a copy in All Mail.

I ran into a related problem to this question during this past week. My Mail app (on my 2017 27inch iMac - latest MacOS) had been having problems for the last month or so similar to other posts I have read concerning continuously moving messages and using large amounts of CPU. I finally found the probable cause - deleted emails were not being cleared from trash and I had over 22,000 of them. I have had the delete trash option for all mailboxes set at 1 month but looks like no clean up had been done since the beginning of July. I also noticed the Archive folder was huge and since I don't use it, I deleted most of it. My Mail app then seemed to start working correctly (and it has been for at least 4 days now).

However, I must have done something wrong when deleting the trash or archived emails because all of the gmail messages in my inbox and sent folders were gone. I haven't had time to check all of my other folders so hoping those are still there. I do have backups so I was able to recover most if not all the messages but still wondering what happened to cause them to be deleted.

You can have an Archive folder with other email providers. For a Gmail account, that is how Apple has decided to implement the All Mail label.

Archive is an IMAP mail feature to protect emails on the server ... On My Mac is a local home folder. The mail exists in both locations unless physically removed.

Correct! IMAP did this to prevent the chaos of deleted emails in the old POP servers.