https://safety.google/privacy/ads-and-data/
> Google does not use keywords or messages in your inbox to show you ads. Nobody reads your email in order to show you ads.
https://www.nytimes.com/2017/06/23/technology/gmail-ads.html
They eventually stopped, although the phrasing of the privacy policy is vague enough that, as wodenokoto mentions above, I wouldn't be surprised if email messages were still scanned for some advertising purposes. The fragment on the page you link to is only about ads shown in Gmail, doesn't exclude using keywords and messages for tracking, classifying etc. (it just doesn't use them "to show you ads") and doesn't actually exclude using programs to process messages (i.e. you can still reasonably say that "nobody reads" messages if you just feed them into a program). It's also not very obvious if "messages in your inbox" also includes messages you send.
FWIW, I think the policy is deliberately open-ended so as to be future-proof, but I doubt emails are an important source of advertising data today, so I think it's likely that Google doesn't rely on it that much anymore. Most sources of legitimate (i.e. non-spam email) that are useful for advertising -- e.g. online shops and the like -- already track you and show you ads, and Google is already deeply embedded there. Millions and millions of personal accounts are an useful strategic asset to have but I think there are better sources of data.
I completely disagree with the first part of your assertion. Email is still the main medium for all organizations, especially private companies taking your money for something, to communicate with you with plenty of details. Be it ordering some product online or booking a flight or other travel ticket or ordering a service or anything else.
The richness and amount of information conveyed over email pales in comparison to SMS notifications. So email is still a treasure trove of what people are doing and have done.
That's true, but all these places already track the living hell out of you. Even the newsletters they send over email have tracking information. By the time they've sent you an email after your first purchase, they know everything they need to show you relevant ads (in fact, that's probably why you made the first purchase...). I doubt bulk analysis of emails can show anything that is not already known way before the emails got sent.
Google can probably serve nice ads just based on metadata it gathers on the SMTP level, without even using the raw message. Someone mails his bank, maybe show some banking related e-mails, etc.
And it would still stay true to the proclamation on that page.
It was never a conspiracy theory. Google used to be very open about the fact that they were scanning emails.
