How to Retrieve all mails present in the all mailboxes in exchange 2010.

Is there way to get all emails from all accounts(Mail Boxes) in exchange server?

 ExchangeService Service = new ExchangeService(ExchangeVersion.Exchange2010);
 Service.Credentials = new WebCredentials("user1", "Password", "constento");
 Service.Url = new Uri("HTTPS://ServerName/EWS/Exchange.asmx");

Here i can get only user1 mailbox mails.How can i get all mails present in the all mailboxes in Exchange by giving single credentials details.Is it possible to do????