This person never agreed to have its email scanned. Never agreed that its email address would become an index key on a profile to serve ads. Never agreed that its writing/attachments, commercial or not, would be part on how Google makes its money.
I've heard about people manipulating HTML forms to submit lower prices when shopping online. What happens if I send a poem that I wrote to a gmail account and append a Terms of Service to it, basically saying if Google scans this email with commercial intent they must pay me money? Is something like this even possible?