[exim] How to go about 'saving bits'

We want to use a filter to save a snippet of information from every
message. Ideally, we would like to save the message sender & recipients
(we store recipients in a variable in the ACL that we can reference) to a
file.

I guess the question is, how can I make a little file for every message
processed and drop some variables into it so we can have an external
process read them later?



Regards,


Rob