I'd like to understand the differences in the envelope fields at points
where external filtering can happen:
* content_filter when receive_override_options=no_address_mappings (sent
to filter via SMTP)
* content_filter when address mappings have occurred (sent to filter via
SMTP)
* in the delivery agent (given to delivery agent via LMTP)
How would a content filter see the envelope fields in these cases? What
fields change? Can adding a X-Original-To header help the delivery agent
see the message as originally received? (Is this possible in Postfix?)
Off-topic part is whether anyone knows the effects any such changes
would have on spam filtering?
I also assume multi-recipient messages would be filtered multiple times
if done in delivery vs. in content_filter.
