Yahoo! Mail
Yahoo! made a deal with the online communications company Four11 for co-branded white pages. Marvin Gavin, who worked at Four11 as the Director of International Business Development, said "We always had a bias about being acquired by Yahoo. They were more entrepreneurial than Microsoft. We had a great cultural fit – it made a lot of sense." In the end, Yahoo! acquired Four11 for $96 million. The purpose behind acquiring Four11 was the company's RocketMail webmail service, which launched in 1997. Yahoo! announced the acquisition on October 8, 1997, close to the time that Yahoo! Mail was launched. Yahoo! chose acquisition rather than internal platform development, because, as Healy said, "Hotmail was growing at thousands and thousands users per week. We did an analysis. For us to build, it would have taken four to six months, and by then, so many users would have taken an email account. The speed of the market was critical."
Windows Live Messenger
On October 13, 2005, Yahoo! and Microsoft announced plans to add interoperability between their messenger services. The announcement came after years of third-party interoperability success (most notably, PowWow by Tribal Voice, Trillian, Pidgin) and criticisms from Tribal Voice and iCast that the major real time communications services were locking their networks. Yahoo! and Windows Live Messenger became interoperable on July 12, 2006. For six years, Yahoo! Messenger and Windows Live Messenger users in possession of up-to-date software could communicate across the two networks. Instant messaging as well as transmission of emoticons, nudges, offline messages, presence information and personal status messages were supported. On December 14, 2012, the interoperability ended.