Shared Address Space for Live@edu

Applies to: Live@edu

Topic Last Modified: 2011-07-06

If you are deploying cloud-based mailboxes to supplement an existing on-premises messaging system, you may want to have a shared address space. A shared address space is when two different messaging systems share the same domain suffix. This configuration is also known as a split domain. The terms "address space" and "domain" are used interchangeably.

Important This topic describes shared address space configuration for Live@edu organizations. For Microsoft Office 365 for enterprises, see Hybrid Routing – Pointing your MX record to the Cloud, and the Exchange Server Deployment Assistant.

Decisions, decisions

As you consider deploying a shared address space between your on-premises messaging system and the cloud-based e-mail service, the fundamental question is: "Where will e-mail arriving from senders on the Internet get delivered first?"

There are two configuration options:

On-premises relay All e-mail sent to recipients in the shared address space by a sender on the Internet is first delivered to the on-premises messaging system. The on-premises messaging system is responsible for forwarding e-mail addressed to recipients in the cloud-based e-mail service. For more information, see Shared Address Space with On-Premises Relay for Live@edu.
Cloud relay All e-mail sent to recipients in the shared address space by a sender on the Internet is first delivered to the cloud-based e-mail service. The cloud-based e-mail service is responsible for forwarding e-mail addressed to recipients in the on-premises messaging system using mail users. For more information, see Shared Address Space with Cloud Relay for Live@edu.

Pros and cons of each option

No shared address space configuration is perfect. Each has its advantages and disadvantages. Carefully consider which configuration best suits the needs of your organization. Here are some things to consider.

Option	Pros	Cons
On-premises relay	Flexibility in how you configure forwarding to recipients in the cloud-based e-mail service. No change to existing mail flow is required for the on-premises messaging system. You can continue to use the existing anti-spam and antivirus solution that protects your on-premises messaging system.	Configuring the solution that forwards e-mail to the cloud-based e-mail service recipients can be difficult to set up and maintain. The on-premises messaging system is responsible for protecting messages that are forwarded to the cloud-based e-mail service from spam and viruses. Failure to do so may cause the e-mail coming from the on-premises messaging system to be blocked or severely throttled by the cloud-based e-mail service.
Cloud relay	Users in the on-premises messaging system are protected by Forefront Online Protection for Exchange.	Changes to the existing mail flow may be required for the on-premises messaging system. You have to install and configure a directory synchronization solution. See Implement Outlook Live Directory Sync for Live@edu.