Migrating form Media Temple IMAP to Google – keep archive of old mail

Hello,

My email host (Media Temple) is being closed down, so I've migrated my account (approx 16,000 emails, but I've only migrated back to 2018; account dates back to around 2012) to Google Workspace. It's working well.

I use Mail as my client and have added my new Gmail account to it - very simple to do and all of my folders and subfolders have carried over pretty well (not perfectly).

I want to maintain my old Media Temple (MT) in Mail so if I ever have to search for an old email, it's available (the account will be deleted from MT in the coming days). The issue I'm having is that when I send/reply from my Gmail account, it's appearing as a new sent item in the MT. I've tried changing the outgoing server on MT to 'None', but then I can't send from my Gmail account either. I've tried unticking 'Enable this account' for MT, but then it disappears from my list.

Is there a way to keep this MT account visible/searchable, but stop it from being active (sending new emails)?

The other query/issue I have is that my Gmail account has created a folder called 'Archive' (see screenshot), which appears to have every email in it. Can I delete this folder? It has ~16,000 in it.

Thanks in advance.