If I were to ascribe a meaning to that failure, it would be, "We haven't seen enough consistent & recent mail flow from your server that gives us confidence that our recipients are likely to want this mail." That said, for the past 3 weeks (at least), Microsoft has been blocking pretty broadly and very rarely changing their mind, even after appropriate appeals to Microsoft Support. I believe they are changing how they process support tickets, but things are currently in chaos.
On Fri, May 22, 2026 at 11:05 AM John Levine via mailop <[email protected]> wrote: > Microsoft/Outlook has been rejecting all the mail from my mailing list > server with this message. > It says temporary, but it's been going on long enough that messages are > timing out and bouncing, > quite possibly a month or more, but I don't have enough MS subscribers > that anyone complained > until recently. > > It's a tiny little server, it's been around for many years, and it's very > unlikely to be > sending mail that users object to. > > 2026-05-22 12:27:31.262250500 delivery 551907: deferral: Connected to > 52.101.40.28 but sender was rejected./Remote host said: 451 4.7.650 > The mail server [192.55.226.75] has been temporarily rate limited due > to IP reputation. For e-mail delivery information, see > https://aka.ms/postmaster (S775) [Name=Protocol Filter > Agent][AGT=PFA][MxId=11BD6DD8C0C7A716] > [CY4PEPF0000E9CF.namprd03.prod.outlook.com 2026-05-22T16:27:31.233Z > 08DEB6EC620C7362]/ > > I tried to add my network 192.55.226.0/24 to SNDS, but it wants to send > the > confirmation mail to [email protected] because their WHOIS lookup is broken, > too > > I renumbered my server a year or so ago and I suppose it's possible they've > been grumpy since then, but other IPs in the same range that send to MS > don't > have that problem. > > R's, > John > _______________________________________________ > mailop mailing list > [email protected] > https://list.mailop.org/listinfo/mailop >
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