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Re: [ietf-smtp] SMTP status codes 251 and 551

2020-02-10 14:11:11
In article <644DAD60BFC9A9FC2C84194A@PSB> you write:
...  I can actually see some advantages for organizations that divide up
their internal mail systems by laboratory or country (and
pressure to do the latter from privacy law differences) when
people make intra-company moves.   But, no, one cannot get rid
of them on the basis of "never implemented or deployed".

That's not what I was planning, although it might be interesting to
try returning some 251 codes and see how well it works.

For an article I'm writing, I'm figuring out what to say about the
slow demise of mail forwarding.

My recollection of the 1980s is that you normally had one e-mail
address.  If you moved, you'd get a new address, perhaps with a
temporary courtesy forward like for paper mail.  There were
distribution lists, but they felt different from normal addresses.  I
don't get the impression there were a lot of role addresses other than

Now there are role addresses, "permanent" forwarding addresses, and
many ISPs let you keep your address even if you stop being a customer
(Comcast and Spectrum in the U.S.)  You'd like them all to forward
mail to the one place you read it, but increasingly it doesn't work.

One issue is naive spam filtering.  Any time a system does forwarding
at scale, some of what's forwarded will be treated as spam because no
two spam filters work the same.  Sensible filters don't block known
forwarders unless something really bad happens.  I hear that a poorly
supervised robot at Proofpoint is currently blocking forwarded mail
from Tucows' large hosted mail system, which in effect makes the mail
disappear.  Dunno if Tucows sends DSNs but if they do a lot of the
senders aren't prepared to deal with them.

Another is DMARC.  I host the mail for my local town government.  Most
of the users read their mail at Gmail, and despite making no
modifications to mail other than adding ARC headers, Gmail rejects a
lot of it due to overstrict sender DMARC policies.  The usual issue is
that they do DMARC on the cheap using only SPF validation, no DKIM,
which of course can't deal with forwarding.

Another large change since the 1980s is that then most people read
their mail on the same computer where the mail was stored, now nobody
does and we all use IMAP.  So I've told the town people how to set up
Gmail to collect mail from a mailbox here and switched back to local
delivery.  That avoids nearly all of the delivery issues since there's
no DMARC checks on fetched mail and for the most part it assumes that
stuff being fetched is OK.


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