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Exchange Server Compatibility Information Exchange Server Version Compatibility 5.5* No 2000 Yes 2003 Yes 2007 Maybe * May Adapt (More Information)

Backup SMTP / MX Server
Author: Simon Butler, Exchange MVP, MCSE

Exchange can be configured to act as a backup MX server for another domain. Your Exchange server would accept email for another domain whose server is down, and then it would send the email on when the server is back in operation.

This will avoid anyone getting delivery failure messages. However you cannot extract the emails from the queue using this method, as it is just a storage point.

However the best use of this method is purely as a backup service after the original has gone down. A dynamic DNS service would be used to point email traffic at the backup server. The setup of the dynamic DNS server has been covered on the authors blog here: The Problem with Backup MX Services and an Alternative (blog - opens in new window)

Internal Network Check

Make sure that you don't have this domain listed in your internal DNS information.

Exchange Configuration

Create a new SMTP Connector in Exchange.

1. Open ESM, Connectors.
2. Right click on Connectors and choose New, SMTP Connector.
3. Give the connector a name that identifies it as the relay for this domain.
4. On the General tab, change the option to "Forward all email through this connector to the following smart hosts" and enter the IP Address or DNS name of the other server in the box for Smart Host. If entering an IP address it needs to be enclosed in [ ]: [192.168.1.1]
5. Under "Local Bridgeheads" add your Exchange server.
6. On the "Address Space" tab, remove the default * and enter the domain name that you wish to store email for.
7. Enable the option "Allow messages to be relayed to these domains"
8. All other options can be left as default.

That should be it. Exchange will accept the email for that server, if it cannot connect to the smart host (the real email server) then the messages will queue. This will be a single queue in ESM.

Increasing Timeouts

If you are backing up a server that will be down for an extended period of time, then change the timeouts on the SMTP virtual server so that email stays in the queues longer. However do monitor the queues as that will affect all email that passes through the Exchange server.