Pairing of security certificates with email accounts

I have three third party email accounts configured for Outlook 2007. A certificate was downoaded and launched today. I find that when sending, the message generated that a certificate did not exist for the email account I am sending from. Could not find how to match up accounts with cerfificates from the documentation. Additionally, not sure if one is allowed to download more than one certificate. Guidance sought

Check that you are running CSE in Outlook Only Mode and also check the settings in Outlook by clicking on Tools>>>Options and then the Security Tab. There’s a little drop down bar where it says Encrypted Mail (Default Setting) your certificate should be listed there so select it (You may have to use the “Settings” button next to the dropdown). Also ensure that both “Encrypt contents…” and “Add digital signature…” are UNTICKED as CSE processes these for you. Restart Outlook and send a test message to yourself.

P.S. Also check that the certificate is installed by going into Internet Explorer Properties and clicking on Content then Certificates. It should be listed there also.