Google and Postini? Makes sense to me. Postini adds vertical integration for Google's outsourced Gmail business. Large companies won't outsource e-mail without security while mid-market companies want turnkey bundled solutions. Now Google has all of the pieces in hand.
The e-mail marriage is obvious but there's more here than meets the eye. Postini has focused on broadening its offering to secure other forms of communication beyond e-mail. For example, Postini has a great portfolio for compliance including e-mail encryption, archival, and policy-enforced TLS. Not very attractive for consumers doing Google searches, but real credible stuff for enterprise organizations struggling to jump over new regulatory hurdles. It is a lot easier to outsource this stuff.
When I heard about this deal I liked it immediately but the price seemed pretty high to me. For $625 million, Google could have offered a small fortune to every spammer in the world rather than grab Postini's e-mail surveillance, cops, and toolbox. Nevertheless, this is pocket change for Google. Google gets the obvious e-mail security and a whole lot of other high value security and compliance services that move it much closer to the enterprise.