When I migrated emails last time, I setup my old email to automatically forward to the new email. Then on my new email, I setup an automatic label for any email that was addressed to the old address. Every week or two I’d review what was sent to it and either update the email address used or unsubscribe. Eventually it got to a level where I wasn’t getting much at the old email anymore and finally deleted it.
It’s a good game. Just don’t take the content warning at the start lightly. I’ve tried to finish it twice but haven’t been able to get more than a couple of hours in.