Mail: problem after re-importing from Gmail

Sorry, it's a strange, long and boring story. I wrongly deleted more than 5.000 emails from an IMAP account and there was no way to import them into Mail (my Mail apps works offly since long time, I dont' know why) as I had a recent backup of the Mail folder on an external disk. I then found the .emlx messages and and imported them into Thunderbird in a particualr folder. The i choose "Copy mails to..." and choose the Incoming messages folder (in TB). The purpose was to upload them to Gmail (as I said this can be done also from mail but my Mail app is not working well, maybe because my High Sierra comes is an update over upddate since El Capitan). While mail where copied into the incoming box they where also uploaded to Gmail. Correctly., I was checking the process throw a browser.

Here came the problem: Mail has dowloaded all both into the Incoming box and the Archive box, duplicating them.

So: as I do not need to have them all "archieved" I tried to delete them from the Archive folder and this is what happens:

- if I delete from the Archive folder i get them deleted immediately also ftom the Inbox folder. I don't want this, of course.

- but if I delete them form the Inbox folder they DON'T get deleted from the Archive folder.

Shouldn't be the opposite, regardless this is a (minor) problem for me?

Look that when are impirted back from Gmail they're tagged also as "archived" but can't get rid of this.

This is not a seriuos issue for me as I'm goingo to migrate once again to TB but I'm an Apple technichan and I need to know how to solve this, as you can understand.

TNX

Simon