John Leslie wrote:
Let's also leave aside the religious arguments about what belongs
in 2821bis. (IMHO, this is largely an operational tuning issue, and
the protocol spec shouldn't try to mandate operational tuning.)
Backscatter is a support nightmare. Unless you can match NDNs to
actual messages sent, many customers will be happiest if you discard
But "discard them all" is against my religion. Professions have their
rules, lawyers don't work for the mob, docs don't help with euthanasia,
hackers don't manipulate data, soldiers don't attack civilians, and
postmasters don't "discard them all".
The same customers could whine if their mail with a typo caused a good
bounce ending up in /dev/discard_them_all. For one of the religions
you don't wish to talk about it is a core dogma to cause good bounces
in a rare scenario decreed to be legit in a closely related religion
you also don't wish to talk about.
On the SMTP list we IMO cannot say that the future SMTP standard is
(only) a religion. It is supposed to be the real thing, replace 821
in STD 10 in about 30 months.
The problem <ietf-smtp> can't seem to face is that the mere
presence of a process listening on port 25 of a particular IP
address says nothing about intent to receive email for a particular
domain which has an A)ddress record pointing to that IP address. An
MX record _does_ state such an intent.
2821 and 2821bis have it clear that the mere presence of a listening
process does not say anything about the intent to receive mail for
the corresponding domains. The MX can say something else, without
MX a listening process at A or AAAA can reject clients or individual
mails as it sees fit.
The problematic situation is the absence of MX and listening process,
senders are forced to wait 100 hours, somebody might find the reboot
button of the affected host. Another problematic situation is mail
claiming to be "from" this domain without MX, receivers cannot wait
until somebody finds the reboot button for a quick plausibility test,
they are forced to reject such suspicious mails temporarily.
Religious operational tuning or not, when receivers accept suspicious
mails "on probation" they didn't read and understand 2821bis, likely following
their own homebrewn "discard them all" strategies.