Please follow these instructions to install your SSL certificate on Microsoft Exchange Server 2003:
Install your SSL Certificate
1. Once you received your SSL certificate by e-mail, please copy and paste it into a text file and save the file with the .crt extension. (Include the tags -----BEGIN CERTIFICATE----- and -----END CERTIFICATE-----).
2. Open Internet Information Services Manager (IIS).
3. Expand Internet Information Services (if needed) and browse to the web site you have a pending certificate request on. Right-click on the site and click Properties.
4. Click the Directory Security tab. Under the Secure Communications Section, click Server Certificate.
5. On the Web Server Certificate Wizard, click Next.
6. Choose to Process the pending request and install the certificate. Click Next.
7. Type in the location of your SSL certificate (from step 1). Click Next twice and click Finish.
Assign your SSL Certificate in Exchange
1. Using the Internet Services Manager, open the properties for the Exchange virtual directory.
2. Select the Directory Security tab and click on the Edit button in the Secure Communication section.
3. In the Secure Communication dialogue box, check the box Require Secure Channel (SSL), you could also check the box Require 128-bit encryption but if you do, any browsers that do not support 128-bit encryption will be unable to connect.