Frank Ellermann writes:
Dick St.Peters wrote:
251-forwarding is extremely rare anyway.
The more important issue is that SPF FAIL breaks the
much-more-common alias forwarding described in RFC 1123
section 5.3.6(a).
ACK, but that's what I mean when I say 251-forwarding,
for some time I wrote 5.3.6(a)-forwarding, 251 is shorter.
In 5.3.6(a) alias forwarding, the return code is 250, not 251.
251 is for telling the sender that the user isn't local but you'll
forward. I believe the intent was a hint to the sender that he/she
should send mail directly if possible. A typical use would be where a
user had moved and changed address.
5.3.6(a) alias forwarding is typically for cases where the sender
should NOT change the address he/she sends to, so there's no need to
inform the sender that the mail is being forwarded. A common use is a
user who is temporarily relocated - on vacation, on assignment, etc.
Another is a user who receives mail at different addresses for
different purposes or businesses and wants to deal with it all from a
single mail account.
--
Dick St.Peters, stpeters(_at_)NetHeaven(_dot_)com