Delete expired/exiting certificates On outlook 2003 is as follows:
1. On the Tools menu, click Options, and then click the Security tab.
2. Click Import/Export Digital ID.
3. Click Export your digital ID to a file.
4. Click Select, and then click the certificate that you want to remove.
5. In the Filename box, enter a path and name for the file, or click Browse.
6. In the Password box, type a password for the file.
7. In the Confirm box, enter the password again.
8. Select the Delete digital ID from system check box.
9. Delete the file you created.
Note You will not be able to open any messages that are encrypted by using the certificate you removed.