1. Make sure that you have imported your certificate into Windows.
2. Open Outlook
3. From the File menu, click the Options menu, select the Trust Center settings button. 
   
4. Click on the Email Security section and select the following options:
   • Add digital signature to outgoing messages
   • Send clear text signed message when sending signed messages
     
     

   

5. For encryption, ITS recommends that you do not select the option to “Encrypt contents and attachments for outgoing messages.” ITS recommends that you manually choose encryption for individual messages rather that setting it by default.

   Note: You can send an encrypted message only if you have the recipient’s public key.

6. Click the Settings button. Outlook displays options for your signing and public encryption certificates under Certificates and Algorithms.  Outlook includes your public signing certificate when it send your signing certificate so that users may send you encrypted messages.
7. Click the Choose button to the right of the Signing Certificate, select your certificate from the list and select OK. 
   
   
   • Select the Hash Algorithm: SHA1
8. Click the Choose button to the right of the Encryption Certificate, select your certificate from the list and click OK. 
   
   • Select the Encryption Algorithm: 3DES or AES 256-BIT (for compatibility with older email clients it may be necessary to select 3DES).
9. Your settings should look like this:
   
10. Click OK to save. 

Other Topics:

• Searching Address Book (GAL) for Certificates - Outlook
• Troubleshooting - Unable to Decrypt Mail Sent from Outlook