[Exim] Piping mail through gpg

Hello,

I need to pipe some mails through gpg.

I have a local account (named admin) that gets all mail coming from the mail
system itself, e.g. cron output or exim error messages. Now I'd like to
forward this mail to an external address, but for this I'd like to pipe the mails
through gpg for encryption.

Any ideas how to do this?

Bye,
Andreas