Are you trying to preserve the Emailactivitykey in both tables?  If so that will not work if there is overlap between the two tables.  Otherwise it looks like your third approach...

If the question is why I work with computers the answer is definitely intrinsic, I've always liked playing with computers and trying to make them do what I want and...

No, losing AD authentication in an Enterprise environment is a huge negative if your company is primarily already a MS shop.

Well you can try to rename the file 😛

In general I don't believe in deleting relevant data, especially after working in places where even seemingly minor records remain relevant and end up being far more important that you'd...