I actually host my own email but every time I send a message to somebody using one of these webmails it gets indexed and monetized.

But I would argue that it's a technical problem first and foremost, email security is mostly a joke. If I need to send sensitive things through emails I can always use PGP to actually protect it, instead of relying on the goodwill of the email provider not to peek into the message. If people really valued their privacy they'd be doing something similar.