Under the FAQ “Do I have to upgrade to the new Yahoo! Mail?” Yahoo notes that,
There are settings that allow users to restrict ads, but there's no way to stop Yahoo from monitoring email content for the purpose of data collection other than using an IMAP client or leaving Yahoo mail. Yahoo is offering prorated refunds to Premium Mail Plus users who want to bail out for any reason.
It's important to stay on top of privacy policies and know what companies are doing with the personal data housed on their servers, but Yahoo is far from the first major email provider to scan messages as part of data mining for targeted ads. Gmail certainly incorporates information about the content of emails to display customised content. Gmail help states:
If you’ve recently received a lot of messages about photography or cameras, a deal from a local camera store might be interesting . . . Ad targeting in Gmail is fully automated, and no humans read your email or Google Account information in order to show you advertisements or related information.
Maybe it's not the scandal of the century, but if you're upgrading from Yahoo Classic (Bueller . . . Bueller) or you've never thought about the ads you're shown alongside your email, now might be a good time to assess. [TechCrunch]