how do I run incoming email through a program when balsa downloads it

[Philip Hunt <cabalamat gmail com>]

Hi,

I have an email account that I'm downloading from using POP3. What I
would like to do is to get Balsa to download the email, send it to a
program I've written, get the output from that program, and then deal
with it in the normal way that Balsa deals with an incoming email.

(In case you're curious, I'm writing an email encryption program that
automatically encrypts on the way out and automatically decrypts on
the way in).

What I would like to happen is that Balsa invokes my program like
this, so it can read ist input from stdin and output it to stdout:

    my_program <incoming_email >processed_incoming_email

where incoming_email is the email as got from the POP3 server, and
processed_incoming_email is the output that my_program produces (for
example incoming_email and it may decrypt it).

Is it possible to do this with Balsa?

I'm trying yto do it through "Filter messages through procmail" but
not having much success. How does Balsa invoke procmail; is it through
stdin/stdout as above, or some other way -- the documentation isn't
clear.

-- 
Phil Hunt, <cabalamat gmail com>