Actually, that's an interesting thought. I have a Gmail account I don't use much, but I almost never access it from the web. I only use it with a mail client. I never see any of the ads they would show if I accessed it through the web. I do wonder now if they'll cut it off. I've been trying to move away from using them at all anyway, so no loss if they do, but certainly an interesting idea.

For a while Gmail would give a browser incompatiblity warning if you were running an adblocker

There is a paid option if you use adblock in google apps for business.

I find the service is actually quite good, but I'm currently investigating moving to protonmail instead.