[exim] exim "appliance"

Hi,

I will begin explore exim as a "smtp gateway appliance" to filter spam,
virus, and apply policies (block profanity, big attachment...).
But I need some help with initial setup on exim.conf.
The idea is deploy the appliance in front a default mta:

internet  -->  exim appliance --> mta --> users
users     -->  mta --> exim appliance --> internet

the address validation of internal users may be flexible: ldap,mysql,text
file.

Any sugestions?

Regards,

Marlon