Trouble encrypting email to co-worker

My co-worker and I are testing out Comodo, seeing if we can adopt it company wide for sending sensitive information more securely. We’ve been able to follow the Secure Email Certificate process and digitally sign our emails, however, it is the encryption that is causing problems. He is able to send me encrypted emails, which I can open and read, but I am not able to encrypt emails back to them.

Thoughts on what I am missing?

thanks,

DjinnD

What happens when you try to reply to his encrypted email with your own encrypted email? Do you get an error? What does the error say?

And what mail clients are you using?

Hi,

If you get any error while encrypting, please submit the ticket in the following link with error screen shot
https://support.comodo.com/index.php?_m=tickets&_a=submit