Is there a solution, paid or otherwise, that would give a Gmail user a plugin that would allow them to determine upon send (or read) whether the email (or thread) would be associated with the CRM contact record?

The inbuilt capability is somewhat an all or nothing approach, and to further fine tune seems complex. The Zoho CRM Gmail plugin is not especially fully featured, in that it is focused on getting contacts or leads into CRM, not actual email correspondence.

We are long-term gSuite users, so not interested in moving to Zoho mail. Are there solutions that do as I describe?

If such a solution doesn't exist, I wonder how difficult it would be to commission someone to do it.