Now that's not very nice. Mega email provider Yahoo isn't honoring users' requests not to track them. To log into Yahoo mail the user has to accept cookies. And after logging out a tiny little notice appears on the page.
Do Not Track is no longer enabled on Yahoo. Your experience is now personalized. More info.
Here's a screen shot:
The "More info" page goes to their privacy page which basically says they'll use your personal info for marketing purposes or to satisfy law enforcement requests. Doesn't the NSA tap their data anyway? That seems to be what the Snowden documents said.
In any event, giving them the benefit of the doubt on that, it's still rude to track customers when they've asked you not to.