I believe the error message is explanatory - and FWIW, they’re enforcing stricter sending guidelines (see https://techcommunity.microsoft.com/blog/microsoftdefenderforoffice365blog/strengthening-email-ecosystem-outlook%e2%80%99s-new-requirements-for-high%e2%80%90volume-senders/4399730 ).
-Udeme On Mon, May 5, 2025 at 10:14 AM Kurt Jaeger via mailop <mailop@mailop.org> wrote: > Hi! > > A mail server I'm happen to manage has lots of problems with > rejects from outlook/hotmail mailservers. > > The error message looks very generic: > > Reason: 550 5.7.1 Unfortunately, messages from [xxx.xxx.xxx.xxx] weren't > sent. Please contact your Internet service provider since part of their > network is on our block list (S3150). You can also refer your provider to > http://mail.live.com/mail/troubleshooting.aspx#errors. [Name=Protocol > Filter Agent][AGT=PFA] > > Many identical cases can be found if one asks a friendly search engine > for 'Protocol Filter Agent'. Most of the are answered with vage > replies by hotmail/outlook support. > > The sending host has dkim, the domain is doing the same since 25 years, > spf is fine, forward/reverse dns is fine. SNDS is active and coming > up empty for the whole range. JMRP is active, no issues as well. > > So what's bugging hotmail/outlook this time ? > > -- > In the nightmare of the dark W.H. Auden, 1940 > all the dogs of Europe bark > p...@opsec.eu +49 171 3101372 > > _______________________________________________ > mailop mailing list > mailop@mailop.org > https://list.mailop.org/listinfo/mailop >
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