The U.S. tech industry has largely declared it is off limits to scan emails for information to sell to advertisers. Yahoo still sees the practice as a potential gold mine.

Yahoo’s owner, the Oath unit of Verizon Communications Inc., has been pitching a service to advertisers that analyzes more than 200 million Yahoo Mail inboxes and the rich user data they contain, searching for clues about what products those users might buy, said people who have attended Oath’s presentations as well as current and former employees of the...