On 09/30/17 04:39, Stuart Henderson wrote:
>> It won't surprise anyone here that I disagree with the assertion that
>> greylisting is in any way outdated. Come back with that assertion when
>> the SMTP RFC is amended to drop the retry requirement.
>
> These senders do retry, but not always from the same source address.
> Are you aware of any requirement in RFC5321 about source addresses
> of retries? I didn't find any when I looked (or even a requirement that
> retries are done over the same IP protocol version).
We had hoped for a clarification of the relevant parts in that RFC
update, but unfortunately the RFC still does not require retrying from
the same IP address. Back when the original was written it may have been
the default assumption that retries would come from the same host, but
even then at least some site would have had more than one outgoing mail
exchanger in place.
> Greylisting still has its place, but with the way email operates today,
> exemptions are unavoidable if you have a requirement to communicate
> reliably with users of many email services. Especially with a strict
> per-host greylisting implementation, where you don't get any benefit
> from the common thing where senders often arrange to retry from within
> the same v4 /24.
Unfortunately some senders (IIRC outlook.com being one) don't
necessarily stay within the same /24, even. That's why we need the
nospamd trick. And this will become incrementally more fun (fsvo) as
more of the traffic moves to IPv6.
--
Peter N. M. Hansteen, member of the first RFC 1149 implementation team
http://bsdly.blogspot.com/ http://www.bsdly.net/ http://www.nuug.no/
"Remember to set the evil bit on all malicious network traffic"
delilah spamd[29949]: 85.152.224.147: disconnected after 42673 seconds.
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