[Exim] secure email

Is it possible to configure exim 4.x so email can be sent to a
specific email address if a secure connection with a client
certificate was used to send the email (the restriction is not desired
for other email addresses)? How would I go about this? I'm trying
to set up a system where information for a database is submitted
via email and processed by a script. I have that working, but want
to make it secure.

Also, can someone point me to a tutorial on how to create client
certificates?

Rossz