Manage Split Domain Routing

Target Audience: Hosted Microsoft Exchange and Rackspace Email users

Split Domain Routing (SDR) allows you to have a single domain's mailboxes distributed between our system and an external system, working together as though they were in one environment.  This is primarily used when migrating a large number of mailboxes over to our system from another server over an extended period of time.  Mailboxes can be moved in batches to make the move more manageable for administrators and to make the transition almost seamless for the users.  Though it is not common, SDR can also be used when you need to maintain some mailboxes on an existing system for an extended period of time or permanently. 

Setting up Split Domain Routing

There are two parts to setting up SDR and they relate to enabling our system and the external system to have two-way communication.

If you are using SDR as part of a migration you will want to keep your MX records for the domain pointing to your existing server, described as your external mail server in this documentation. Once the migration is complete you can switch them to us.  If SDR will be a permanent feature of your set up they can point to either your external mail server or us. You may want to point your MX records to Rackspace because then all your messages get the benefit of our spam/anti-virus filtering instead of just the Rackspace-hosted mailboxes.

This diagram shows the message routing for a set up where the MX records for the domain point to Rackspace.

1. Enable Split Domain Routing in the Email & Apps control panel

When SDR is enabled, our environment will forward to your external server any messages addressed to recipients on your domain that do not exist in our system. To enable it requires the hostname of your external mail server (usually one of the MX Records that point to your external system) and a valid email address within the designated domain hosted on that external mail server. We will use this address only to validate the server.  You must also open port 25 on the external mail server so that our system can connect to it.

This diagram shows how messages are routed from Rackspace to your external system once split domain routing is turned on in the control panel.

To enable split domain routing, log into the control panel, and perform the following steps:

 a.  Mouse over the Go to section drop-down menu and select Domains.

   b.  In the Tools section, click the Split Domain link.

   c.  Select the domain for which you want to set up split domain routing.

   d.  Check the Enable Split Domain Routing box.

   e.  In the External Mail Server box, enter the name of your external mail server.

   f.  In the Verification Address box, enter a valid email address that is hosted on your external mail server.

   g.  Click the Save button.

2. Configure Split Domain Routing from your External System to Rackspace

There are two methods for configuring this. One method is to set up split domain routing on the external system using a similar process to our control panel whereby a shared address space is created. The second method is to use sub-domain message routing.

a. Set up split domain routing on your external server

This type of functionality is known by several names including non-authoritative mail delivery and message routing for a shared address space.

The idea is to set up the external server so that if it is not able to deliver a message locally the server forwards to another system.  Different mail systems will have their own procedures for configuring this.

The following Microsoft articles show how to set this up on Exchange 2007 and Exchange 2010:

Exchange Server 2007:  http://technet.microsoft.com/en-us/library/bb676395%28EXCHG.80%29.aspx

Exchange Server 2010:  http://technet.microsoft.com/en-us/library/bb676395.aspx

b. Sub-domain Message Routing

Sub-domain routing uses contacts set up on your external system to forward the messages to a sub-domain e-mail address that has been added as a domain alias on our system. To make this work the following things must be set up:

• a sub-domain is created e.g. rackspace.example.com with MX records pointing to Rackspace.
• rackspace.example.com is added as a domain alias, on our system, for example.com
• contacts (aliases) must be created on the external system for each mailbox hosted by Rackspace - the contact must forward the example.com address to the rackspace.example.com address.

This diagram shows how a message is routing using a contact (alias) to forward the message to the sub-domain address.  

I. Create (or have your DNS host create) a sub-domain (e.g. rackspace.example.com) and point its MX Records to Rackspace. If we host your DNS, enter this sub-domain name in the Mail Records (MX) section of the DNS Settings page in the Control Panel. To learn more, please see the help topic, Manage DNS Records.

Note: For a migration, when changing the MX Records, ensure that you are changing them for the new sub-domain, e.g. rackspace.example.com, and not the primary domain. After all mailboxes are on our system, you will change the MX Records for the primary domain.

II. In our system, the sub-domain must be added as a domain alias for your primary domain name. Please see the help topic, Add Domain Alias for details on how this is done.

III. On the external server, create contacts (also know as aliases) for all of the mailboxes that are hosted on our servers.The aliases should point to the sub-domain. For example, if you have moved the mailbox for john@example.comto our servers, create the alias john@example.com pointing to john@rackspace.example.com on your external server.