Hosted Exchange Server, two main options 
Microsoft Exchange Server is the most widely deployed e-mail servers used in business and have continuously from the first release to the current version Microsoft Exchange Server 2010. The proliferation of Hosting companies, Data Centers and Co-location facilities has increase access to these resources for many small businesses. The two main solutions for Hosted Exchange server; public Hosted Exchange and private Hosted Exchange server which the differences will be explained next.
Public Hosted Exchange - is a large exchange server implementation that hosts multiple companies in one database. The main advantage of this type of configuration is that is is very cost effective and widely available, giving all of the best features of Microsoft Exchange server for $9 -$25 per user per month. This implementation comes without the cost of owning and maintaining the equipment and purchasing licensing.
The main drawback to public hosted Exchange server is the fact that your email resides on the same server as other companies. This becomes a major issue if you ever want to move your service to another provider or bring it in house. Additionally, recovery can take much longer as there is limited ability to move your company email into its own Exchange Storage group. This form of Hosted Exchange may also have problems meeting compliance regulations.
As a Small to midsized IT Solution provider we lose a lot of control over email using this method. Once we verify the email has left the machine there is little we can do to troubleshoot other than getting on the phone and hoping to be able to get someone on the other end to create a support ticket.
Private Hosted Exchange is an Exchange Server that is hosted at a data center or Co-Location facility on either dedicated physical or shared infrastructure hardware. Using shared infrastructure in this environment meets compliance regulations because while the resources are shared, they are secured and run in a single instance where your company is on its own dedicated server instance. The benefit of clustering host servers and redundant SAN back-ends offers Highly Available configuration while hosting in a data center offers the reliability of clean consistent power, cooling and redundant Internet connections. Additionally, the ability to purchase licensing on a monthly as used model offers benefits of Operating expense vs. Capital expenditure.
The main drawback of Private hosted Exchange is cost. There isn't the cost savings of thousands of users sharing the cost of the hardware and hosting.
The control perspective from a Small to midsized IT Solution provider in this senario, we gain total control over email using this method with the ability to follow messaging all the way through the creation to delivery. Network Essentials also has a N+1 Highly available Network / Server infrastructure with the ability to add multiple site redundancy.
Contact Network Essentials to talk about your e-mail needs