Supporting Messaging Clients

Enable Reverse DNS Lookup

If you select this option, Exchange will attempt to verify that the client's IP address matches the host/domain submitted by the client in the EHLO/HELO command. If the reverse DNS lookup is successful, the Received header will remain intact. If the verification is unsuccessful, "unverified" appears after the IP address in the Received header of the message.

To enable reverse DNS lookup

  1. Start System Manager
    On the Start menu, point to Programs, point to Microsoft Exchange, and then click System Manager.
  2. Navigate to the SMTP virtual server.
    1. Servers
    2. Server
    3. Protocols
    4. SMTP
    5. SMTP virtual servers
    6. SMTP virtual server
  3. Right-click the SMTP virtual server, and then click Properties.
  4. On the Delivery tab, click Advanced.
  5. In Advanced Delivery, select the Perform reverse DNS lookup on incoming messages check box.

Note   Because this feature verifies addresses for all incoming messages, its use can affect your Exchange server's performance. Clear the check box to disable the feature.