Citing a jump in complaints about hacked accounts, BT is abandoning Yahoo Mail (YHOO) as the e-mail platform for its broadband services in favor of home-grown BT Mail. 6M Yahoo Mail accounts will be migrated. Meanwhile, Tumblr continues to roll out fresh ad formats. A month after adding sponsored posts (similar to Facebook's Sponsored Stories) to its mobile apps, Tumblr has brought them to its Web dashboard; initial partners include Ford, AT&T, and Viacom. Marissa Mayer has stated Tumblr could see premium and retargeted ads, and Tumblr CEO David Karp has touted his service's potential to enable "creative brand advertising" that breaks traditional display ad molds.