Mail relaying can occur when users outside the organisation use your mail system to send messages bound for another organisation. However, Exchange Server normally prevents unauthorised users and computers from relaying mail through your organisation and this is the behaviour that you'll typically want to use. In this way, only users and computers that are able to authenticate themselves can use your mail system to relay messages.
If necessary, you can grant or deny relaying permissions, overriding the default configuration. To do this, follow these steps:

1. Start System Manager. If administrative groups are enabled, expand the administrative group in which the server you want to use is located.
2. In the console tree, navigate to the Protocols container. Expand Servers, expand the server you want to work with, and then expand Protocols.
3. In the console tree, expand SMTP. Right-click the virtual server that you want to work with, and select Properties.
4. Click the Access tab, and then click Relay. You should now see the Relay Restrictions dialog box, shown below.
   
   If necessary, you can use the Relay Restrictions dialog box to grant some computers the right to relay mail through your organisation.
5. To grant relay rights to specific computers and deny relay rights to all others, click Only The List Below.
6. To deny relaying for specific computers and grant all others the right to relay, click All Except The List Below.
7. Create the grant or deny list. Click Add, and then in the Computer dialog box specify Single Computer, Group Of Computers, or Domain.
   • For a single computer, type the IP address for the computer, such as 192.168.5.50.
   • For groups of computers, type the subnet address, such as 192.168.5, and the subnet mask, such as 255.255.0.0.
   • With a domain name, type the fully qualified domain name, such as eng.domain.com.
   Caution: When you grant or deny relaying by domain, Exchange 2000 Server must perform a reverse DNS lookup on each connection to determine if the connection comes from the domain. These reverse lookups can severely affect the performance of Exchange Server, and this performance impact increases as the number of concurrent users and connections increases.
8. If you want to remove an entry from the grant or deny list, select the entry in the Computers list, and then click Remove.
9. Click OK.

The information in this article applies to:

• Microsoft Exchange 2000 Server