Exchange is Microsoft's entry into the email/groupware server space. It makes it easy for users to communicate and collaborate over the Internet and/or Intranet using a variety of clients on various desktop operating systems.
Exchange Web Site Hosting is available for customers who have a need for the features available from Microsoft Exchange, but do not have the facilities and/or expertise required to host the system themselves. By subscribing with an Exchange Web Site Host provider, the customer can take advantage of all of the benefits of Exchange, without the additional hassle that is involved in maintaining such a system.
Organizations with a need for robust email and collaboration can benefit greatly by using for using the features of Microsoft Exchange within their business. Smaller companies that do not have the IT staff, or the facilities to create and maintain an Exchange network are perfect candidates for working with an Exchange host provider.
That would depend on the your particular usage of the server. Normally, an Exchange hosting provider will set up several Exchange accounts for several companies on the same box, similar to shared web hosting. Customers with higher volume requirements, or who wish to be segregated from the other customers can opt for a dedicated Exchange server. This is nominally more expensive than shared Exchange hosting, but does have its obvious advantages. A dedicated Exchange server is usually suggested for any Exchange hosting account that exceeds 100 users.
These features depend greatly on the Web Site hosting provider. Firstly, all of the functionality of Microsoft Outlook is immediately shared between your users. Calendars, Files, Folders, Tasks, Contact Lists, Address Books all become integrated and sharable among all users of Exchange. Advanced features such as Virus Scanning and Instant Message can normally be made available at an additional price.