Yesterday we announced that we've completed upgrading all Hotmail customers to Outlook.com. Coupled with the growing organic excitement for Outlook.com, this has pushed us to over 400 million active Outlook.com accounts, including 125 million that are accessing email, calendar and contacts on a mobile device using Exchange ActiveSync.

See the full report and details at http://blogs.office.com/b/microsoft-outlook/archive/2013/05/02/outlook-com-400-million-active-accounts-hotmail-upgrade-complete-and-more-features-on-the-way.aspx.