Recipient filtering in Exchange 2003

It’s pointless to process emails for users not present in the Active Directory, as this places a strain on the server, takes up space and generates an unnecessary bounce, whereas it’s so much simpler to reject invalid recipients at the of the MTA rather than afterwards on the MDA, as is the default with Exchange 2003. This default configuration should be avoided for the reasons described in our article Mail server configuration and recipient filtering. This procedure pragmatically describes the configuration to be carried out on a Windows Server EXCHANGE 2003 mail server to set up recipient filtering for Exchange 2003 versions (>6.0.3790.3959).

Create a recipient filter
When using recipient filtering, you can filter messages addressed to e-mail addresses that do not exist in your organization. Recipient filtering only applies to messages from anonymous connections.

To create a recipient filter, proceed as follows:
1. Start Exchange System Manager.
2. Expand Global settings, right-click on Message delivery, then click on Properties.
3. Click on the Recipient filtering tab.
4. To filter e-mail according to a specific e-mail address, click on Add, type in the e-mail address, then click on OK.
5. To filter messages addressed to e-mail addresses that do not exist in your organization, activate the Filter recipients not in directory checkbox.

Apply recipient filter to appropriate SMTP virtual servers
You must enable recipient filters on each SMTP virtual server to which you wish to apply these settings. To apply a filter to an SMTP virtual server, proceed as follows:
1. Start Exchange System Manager.
2. Expand Servers, Server_name, Protocols and then SMTP.
3. Right-click on the SMTP virtual server to which you wish to apply the filter, then click on Properties.
4. In the General tab, click on Advanced options.
5. Click on the IP address to which you wish to apply the filter, then on Modify.
6. In the Identification dialog box, activate the Apply recipient filter checkbox.
7. Click OK twice, then Apply, then OK again.
8. Restart the SMTP virtual server on which you applied the filter.
9. Repeat steps 2 to 8 for each virtual server on which you wish to apply the filter.

This forces the SMTP router to respond immediately with a 550 rejection message, rather than accepting the mail in SMTP and then sending back a bounce, which is increasingly frowned upon…