Re: [ietf-smtp] SMTP status codes 251 and 551
"John Levine" <johnl@taugh.com> Mon, 10 February 2020 20:11 UTC
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From: John Levine <johnl@taugh.com>
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Subject: Re: [ietf-smtp] SMTP status codes 251 and 551
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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 postmaster. 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. R's, John
- [ietf-smtp] SMTP status codes 251 and 551 John R Levine
- Re: [ietf-smtp] SMTP status codes 251 and 551 John C Klensin
- Re: [ietf-smtp] SMTP status codes 251 and 551 John Levine
- Re: [ietf-smtp] SMTP status codes 251 and 551 Kurt Andersen (b)
- Re: [ietf-smtp] SMTP status codes 251 and 551 John R. Levine
- Re: [ietf-smtp] SMTP status codes 251 and 551 George Schlossnagle
- Re: [ietf-smtp] SMTP status codes 251 and 551 John Levine
- Re: [ietf-smtp] SMTP status codes 251 and 551 Alessandro Vesely
- Re: [ietf-smtp] SMTP status codes 251 and 551 Sebastian Hagedorn
- Re: [ietf-smtp] SMTP status codes 251 and 551 Jeremy Harris
- Re: [ietf-smtp] SMTP status codes 251 and 551 Arnt Gulbrandsen
- Re: [ietf-smtp] SMTP status codes 251 and 551 Viktor Dukhovni
- Re: [ietf-smtp] SMTP status codes 251 and 551 Alessandro Vesely