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Username Change

This is one of techniques that we can do for you - if you are in the UK and have remote access to both servers. Contact us for more information.

You may come to a situation where you have two separate Exchange or SBS servers that need to share the same public domain name. If you cannot find a way to connect the sites and merge them in to a single domain and Exchange organisation then you need to find a solution that allows email to flow between the sites.

The solution outlined on this page is one that works, however it doesn't scale very well. Once you get above three or four and you should start to consider merging in to one domain and one Exchange organisation - which is how Exchange is designed to work.

Server Configuration

1. Decide which server is going to be the primary. This is the one that will receive all the email. You can use one of the others for a secondary server if you wish. In this example, London is Primary, Paris is secondary.
2. Setup MX records for your primary domain pointing to these servers, remembering to get the weighting correct.
3. Create a recipient policy (if it doesn't already exist) on each server for your primary domain. Make sure that the option about exchange being responsible for all email delivery to this address is enabled. It should be the primary recipient policy.
4. Create sub domains for each site in the DNS of each server.
   Therefore if you had three sites of London, Paris and Madrid then you would have
   • london.domain.com
   • paris.domain.com
   • madrid.domain.com
5. While working in the internal DNS of each server, create MX records with the external IP address of the other server.
   Therefore the London site will have DNS zones for paris.domain.com and madrid.domain.com and in those will be a DNS entry for mail.paris.domain.com and mail.madrid.domain.com. Each of those would also be set as MX records.
   These MX records do NOT appear on the Internet, but traffic will flow on them because your local machine is looking up the MX records from the location DNS.
6. On each server, add a new additional recipient policy - but don't make it default. This new recipient policy should match the location.
   Continuing with our example:
   • In London, it would be london.domain.com
   • In Paris it would be paris.domain.com
   • In Madrid it would be madrid.domain.com

   The key is that it should NOT be the default policy on any site.

The result of this should be that all users have two email addresses - the default one ending in domain.com and a secondary one that ends location.domain.com.

NOTE: It is important that your DNS is configured correctly. The server should be configured to use your active directory domain controllers for DNS - no external DNS servers should be used.
If you need to use external DNS servers for performance reasons then configure these as forwarders on the active directory DNS servers.

Adding the Remote Users

On the primary server create a mail enabled contact for all users located on the other servers. When creating the contact, initially put in the email address for it's home address (london.domain.com). Once created, wait a moment for recipient policy to stamp the account. You should find that the contact now has two email addresses, @domain.com and @london.domain.com. Do not add local users as they will already have an email address.

Repeat on the other two servers.

• London will have mail enabled contacts for Paris and Madrid.
• Paris will have mail enabled contacts for London and Madrid.
• Madrid will have mail enabled contacts for London and Paris.

Sanity Check
As this can cause an email loop if not configured correctly, there is a sanity check that you can make to ensure that you have it correct.
On the properties of the contact, click on the tab "Exchange General". In the email address box, it should say smtp then username@location.domain.com. If it says username@domain.com then it is wrong and needs to be changed.
On the email addresses tab, the default email address should be @location.domain.com

End Result - Features and Benefits

The net result of this procedure is

• Email for your primary domain can be delivered to any server and it will be routed correctly this is useful for backup queuing of email if the other server is down.
• Users can type in the full public email address (username@domain.com) from any site and it will be routed correctly.
• Users from all three sites will appear in the GAL.
• You can create distribution lists on all three sites with the same membership.
• By using mail enabled contacts the email destined for the other sites is not stored on your server - taking up no storage space on the server.
• The sites only need an internet connection - no direct site connection required.

It can take a while to initially configure, but once done, very easy to maintain if you have limited servers.

SMTP Connectors

If you are using an SMTP Connector to send email, then this can complicate matters. It does depend on what the connector is being used for.

If the connector is being used simply for sending email by DNS, then you don't need to change anything. The server will do a DNS lookup as normal and send the email using the information that it finds.

However if you are using an SMTP connector to send email via a smart host because you are on a DSL connection, then adjust the existing connector. On the namespace tab, change the cost to 10. Then create a new SMTP Connector, add in the address space all of the remote locations and set the cost as 1. Leave the option to use DNS, not a smart host. The connector will then use a direct connection (found from your internal DNS) for inter-site traffic and the settings on the original SMTP connector for all other email.

If you are using an SMTP Connector because you have no other option - usually because your ISP blocks connections to port 25 (smtp) on any server other their own, you will have to adjust this solution. You will have two options.

1. Setup a VPN between the other sites. Then configure an SMTP Connector with a lower cost using the internet IP address or dns name (that resolves to an internal IP address) as the smart host.
2. Adjust your public DNS settings at your domain name registrar to make the sub domains valid on the Internet. They will also require MX records pointing to the relevant server.

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