A rich hosted Exchange environment for every user without having to manage a server.
http://www.microsoft.com/exchange/en-us/exchange-online-hosted-email.aspx
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Get access to data on 7,441,058 websites that are Microsoft Exchange Online Customers. We know of 2,000,001 live websites using Microsoft Exchange Online and an additional 5,441,057 sites that used Microsoft Exchange Online historically and 1,178,930 websites in the United States.
Get a list of 7,441,058 websites using Microsoft Exchange Online which includes location information, hosting data, contact details, 2,000,001 currently live websites and an additional 1,512,903 domains that redirect to sites in this list. 5,441,057 sites that used this technology previously and 1,178,930 websites in the United States currently using Microsoft Exchange Online.