I don't like that Google would build a profile on me by scanning the contents of my emails, but it's an agreement I knowingly enter into when I occasionally use

I don't like that Google would build a profile on me by scanning the contents of my emails, but it's an agreement I knowingly enter into when I occasionally use Gmail. But what about a non-Gmail-using party who sends emails to one or more Gmail users? Is Google building a dossier on them based on their return address? Are they associating that person's email with other tracking mechanisms Google employs? I don't know if Google does these things, but if they did, would it be OK? If some or all of the collected raw data is at most a 'probably foreign' request away for military spies, is it OK to scan and store every bit of data that would be permissible in a mutual-trust-based civil society?