It's appears free, but advertising companies pay Google so they don't have to charge you for the cost of running Gmail https://support.google.com/mail/answer/66

It's appears free, but advertising companies pay Google so they don't have to charge you for the cost of running Gmail https://support.google.com/mail/answer/6603 https://support.google.com/mail/answer/6603. And clients of those advertisers charge their customers (mostly retail) for their ad expenses as a % of their sold goods and services. So we're all paying your Gmail, society is your patron and you're a free rider. That what "I don't care" mean. I'm happy to pay my ESP so you don't have to and so they don't collect your email data (as sender or recipient). You're welcome.