Office 365, Microsoft’s subscription-based solution for hosted email and office productivity tools celebrated it’s official Office 365 First Birthday on June 28, 2012. However, Office 365 is just the latest iteration of hosted services from Microsoft.
As far back as 2003 Microsoft was exploring the opportunities for hosted Exchange. By 2007 they had started rolling out hosted Exchange, and in late 2008 they officially announced BPOS.
I have several customers that have already transitioned to Office 365, or are exploring this as a viable alternative to an on-premise Exchange.
Happy birthday, Office 365!