Twitter advertisers can now employ their email lists and user cookie IDs in order to target a person who has visited their Web properties. It's a move that appears to be Twitter's e-commerce answer to its recently introduced branding-minded "Amplify TV" platform.

At any rate, while the cookies-based retargeting might be new to Twitter, the idea certainly isn't ground-breaking among digital advertising players. On the other hand, targeting social ads based on email lists seems like a new frontier that could get privacy hawks chirping. Conversely, email remains a powerful marketing tool. Since few digital signals suggest purchase intent like an email opt-in, Twitter's move carries huge potential—especially for the direct-response crowd.

In a blog post today, Kevin Weil, senior director of product, revenue for San Francisco-based Twitter, addressed some of the potential privacy concerns, saying it will only use "scrambled, unreadable email address (a hash) or browser-related information (a browser cookie ID). We can then match that information to accounts in order to show them a Promoted Tweet with [an offer]. This is how most other companies handle this practice, and we don’t give advertisers any additional user information."

Twitter users can opt out of the targeting by unchecking the "promoted content" module in their accounts. But initially, they will be auto opt-ins.

Per Weil's post, his company "supports Do Not Track (DNT), Twitter will not receive browser-related information from our ad partners for tailoring ads if users have DNT enabled in their browser."