Keith Moore <moore(_at_)cs(_dot_)utk(_dot_)edu> writes:
Note that the ones that don't add return-path are in violation of
over 20+ years of mail specificatons. See RFC 821 (top of page 22),
RFC 1123 (section 5.3.3 among others), and RFC 2821 (section 4.4).
However there's no guarantee that Return-Path is either consistent
for all messages sent to a list, nor that it is uniquely associated
with a list.
In practice, however, both are true, almost 100% of the time. Even
when various bounce schemes are used, simple regexps almost always
catch them.
--
Perry E. Metzger perry(_at_)piermont(_dot_)com