They used to scan mail - or at least have an option for that in gmail - to show relevant ads in Gmail.

They stopped doing it years ago I think.

Also even on those days the ads were only for the page where you were reading that specific email, it didn't go into a hidden profile that carries over.

Google is actually very privacy councious when it comes to their own properties. Where I agree they fault is with their double click cookie that follows you around the internet