Guuuysss!!!
Could it be this simple? I just tested this and it seemed to work.
In your inbox, you can select your log and track settings. If you get rid of logging new contacts, it won’t create it in your CRM.
Basically, you only want to log emails for exisiting contacts… these are either inbound leads or leads you have uploaded yourself as qualified to be in the system.
It seems to be working for me… hope it helps you!