I've been experimenting with Hashcash (
http://www.hashcash.org). I'm
interested in having exim add Hashcash headers in the course of routing
and transport. I've written an exim transport_filter that can do this
easily. The problem is that it adds a Hashcash header for every address
in the $pipe_addresses list; not only the To and Cc recipients, but also
the Bcc recipients. This means, of course, that although the Bcc header
itself doesn't appear, the BCC'd recipient's address still appears in a
Hashcash header.
One solution that I considered is setting max_rcpt = 1 for the smtp
transport, so that it would never send a batch message to more than one
recipient. This seems needlessly wasteful, however, in the most common
case where a single message to the entire To and Cc list is acceptable.
A reasonable compromise would be to send a batch message to the list of
To and Cc recipients, and then a single message to each of the Bcc
recipients.
There's probably some configuration of built-in exim routers and
transports -- plus maybe a custom pipe or two -- that would make this
possible. This is where I get stuck, though. Am I barking up the wrong
tree? Any suggestions?
Thanks,
Tim.
