SAN FRANCISCO – Microsoft is so confident it has the Internet's best email service that it is about to spend at least $30 million to send its message across the U.S.

The barrage begins Tuesday when Microsoft's twist on email, Outlook.com, escalates an assault on rival services from Google Inc., Yahoo Inc., AOL Inc. and a long list of Internet service providers.

As part of the process, all users of Microsoft's Hotmail and other email services operating under different domains such as MSN.com will be automatically converted to Outlook.com by the summer, if they don't voluntarily switch before then. All the old messages, contacts and settings in the old inboxes will be exported to Outlook.com. Users will also be able to keep their old addresses.