The barrage begins Tuesday when Microsoft's twist on email, Outlook.com, escalates an assault on rival services such as Google's Gmail.
After keeping Outlook.com in a "preview" phase since July 31, Microsoft is ready to accept all comers.
To welcome new users, Microsoft is financing what it believes to be the biggest marketing blitz in the history of email. Outlook.com will be featured in ads running on primetime TV, radio stations, websites, billboards and buses.
Microsoft expects to spend somewhere between $30 million to $90 million on the Outlook campaign, which will run for at least three months.