Developer mailing list delivery issue

[Stuart Henderson]

On 2024/10/24 10:26, Jochen Bern wrote:
> On 24.10.24 02:06, Mabry Tyson wrote:
> > I [...] sent mail to openssh at openssh.com but the mail was not delivered.
> > 24 hours after I sent email to that address, I got a DSN indicating
> > 
> > > Remote server returned '550 5.4.300 Message expired -> 451
> > > Temporary failure, please try again later.'
> 
> ... yeaaahhh whatever it takes to convince the MX that it's *not* talking
> to a spammer, I haven't got it, either ...
> 
> > $ host -t mx openssh.com
> > openssh.com mail is handled by 5 mail.openbsd.org.
> 
> > $ openssl s_client -connect mail.openbsd.org:25 -starttls smtp -servername mail.openbsd.org -quiet
> > Connecting to 199.185.178.25
> [...]
> > 250 STARTTLS
> > EHLO bern.binect.de
> > 250 Hello, spam sender. Pleased to be wasting your time.
> > MAIL FROM:<jochen.bern at binect.de>
> > 250 You are about to try to deliver spam. Your time will be spent, for nothing.
> > rCPT TO:<openssh at openssh.com>
> > 250 This is hurting you more than it is hurting me.
> > DATA
> > 451 Temporary failure, please try again later.
> [connection closed by the server side]

It's greylisting; retrying from the same IP (after expiry of whatever
delay was configured by the admin) should allow it to get through on the
following attempt.

outlook.com are probably not retrying from the same IP.

There's a good chance the admin of the list server is allowing IPs
listed in SPF records of some common domains like outlook.com to bypass
greylisting. There's also a good chance that outlook.com have started
using some new addresses without updating SPF.