For spam, yes. But does it implicitly allow Google to scan for building a user profile of a gmail user ? And of a sender from a different service ? Why would

For spam, yes. But does it implicitly allow Google to scan for building a user profile of a gmail user ? And of a sender from a different service ? Why would google be allowed to build a johnchristopher@fastmail ad profile based on the mail sent to my gmail correspondents ? The analogy with snail mail is blurry because every snail mail exchange doesn't include the full transcript of the conversation.