How to read yahoo mail received from a Comodo encrypted Outlook 2003 e-mail

I have sent an Outlook 2003 e-mail with 2 attached files using CSE with medium encryption to my yahoo mail account.

Yahoo mail received the Outlook e-mail with a single smime.p7m file attached.
When I try to open the attachment it asks me what program I should use to open the file. I’ve tried several programs but none seem to do the job, including CSE.

I have read on CSE’s Help Screen that the web based email should be received with a message from Comodo “Creating Trust Online” giving instructions on how to open the email.

My yahoo mail was received without these instructions. I tried forwarding the yahoo mail to as directed on CSE’s help screen. I never got a reply back from Comodo.

What am I doing wrong?