Dave Crocker wrote:
why is modification of the return path required?
It's only required when forwarding mail to a 3rd party
(or "to another ADMD" in email-arch terminolgy), as it
indicates the transfer of responsibilty as outlined in
RFC 821.
Preserving the spirit of RFC 821 without reverse routes
is a black art. But ignoring it results in backscatter.
Frank