No contents sent in signed certificate


Can anyone please help!

I use Outlook 2013, and the Comodo Certificates were automatically and successfully installed by Chrome Browser.

But, when I send a digitally signed message:

  1. I get a message: The server you are connected to is using a security certificate that cannot be verified. So, every time I need to install the certificate.

  2. After sending it shows a Padlock on the email in the “Sent Items” and not “digitally signed certificate”.

  3. But the recipient receives the email without any content or nothing is visible nor any attachments if any were sent with it.

What am I doing wrong?

Thank you in advance.