Keep Exchange In-House and in the Cloud With Coexistence

With Exchange coexistence, you can keep some of the advantages of a local messaging server installation while gaining the advantages of cloud computing. Find out if it's for you.

 By Jabez Gan
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Organizations interested in some of the benefits of cloud computing have the option to run Exchange Servers in-house, but host mailboxes at Microsoft's data center. This is known as "co-existence," and it has its pros and cons, both from an IT manager's and end user's perspective. In this article, we'll consider the the implications of co-existence for both groups.

The advantages of Exchange coexistence

The advantages of Exchange coexistence can be enumerated by looking at the benefits of each half a coexistence deployment.

An on-premises Exchange server managed by in-house IT enjoys these advantages:

  • Local emails sent/received more quickly
  • Lower WAN bandwidth requirements for HQ users
  • Data leakage minimized
  • Predictable maintenance

An off-premises Exchange server managed by Microsoft enjoys these advantages:

  • Cheaper hardware maintenance
  • Lower WAN bandwidth requirement (if lots of mobile users)
  • Highly secured
  • Predictable cost
  • Datacenter/Hardware redundancy

Let's consider these advantages in more detail:

On-premise Exchange: Full control and faster performance

  1. Frequently used email recipients: Most emails that users send out are addressed to their colleagues, which usually reside in the same mail server or local network. By routing these emails within the same intranet insures faster delivery.
  2. Less bandwidth: Depending on the email usage pattern of the users, having on-premise means less WAN bandwidth needed.
  3. Confidential data stays within the network: Having everything on-premise ensures that confidential emails between colleagues stay within the company's network.
  4. Maintenance period is transparent
  5. IT and management needs to know what's happening with the IT infrastructure. Usually having things outsourced means that we only can rely on the reports by the vendor, and the downtime is beyond the customer's control.

Off-premises Exchange: Services managed by the experts

  1. Lower cost: Paying a small fee to get features like hardware redundancy, datacenter redundancy and managed support is a no brainer. What more do you want when you do not need to setup and maintain these infrastructure.
  2. Very secure: Microsoft's datacenter is equipped with 7 layers of defense-in-depth, from the physical layer to the network layer to the application layer, ensuring that each and every layer is protected with the necessary security.
  3. Predictable budgeting: You know how much email and other IT services will cost you every year. There will not be yearly hardware upgrades or maintenance for the mission critical applications. Management will be able to foresee and allocate the appropriate budget for mission critical applications.
  4. Redundancy for natural disaster: Microsoft has the firepower to ensure that customers' data are replicated throughout a few datacenters around the world. This is to ensure redundancy of data if anything happens to one location. This infrastructure is not something that any companies can afford to build.

The disadvantages of Exchange Coexistence

Deploying either on-premise or using hosted emails have its benefits, but when you combine them together, it also means increased cost. Here are some disadvantages to consider:

  1. Increased cost: Organizations are no longer paying only for costs incurred for their on-premise Exchange; they are also paying for hosted infrastructure. Organizations will be paying twice the money to use email facilities, and this usually will trigger CFO's attention.
  2. Increased management: There's only one way to manage Microsoft Online Services: Log support tickets. If you have an issue, you log a support ticket for Microsoft Online Support to assist. Now that you have both Microsoft Online Services and on-premise, it means IT will have double work as they will need to manage both on-premise and Microsoft Online Services support tickets.
  3. Increased complexity: Co-existence involves integration of two different systems. If the bridge server (the server which copies the email from the local server to the remote server) goes down, emails will be affected. The ability to manage this kind of infrastructure requires IT that has good foundations of how email infrastructure works.
This article was originally published on Feb 16, 2011
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