If you search this mailing list, you will see posts from a Microsoft employee that says:
"S3150 and S3140 are both volume (emails per hour) throttling.” and "S 3150 is a throttle block, possibly related to IP reputation classification. It should automatically expire on its own, and is generally caused by sending too much traffic too fast.” So you may want to try sending slower. Don’t open too many connections to MS at one time and limit the amount of mail you send per connection. laura > On 24 Sep 2025, at 10:04, Boris Pavlov via mailop <[email protected]> wrote: > > Hello everyone, > > I'm reaching out to ask if anyone on this list may have contacts at Microsoft > who could help us escalate a persistent deliverability issue. > > Since last Thursday, more than 40 IPs from the same range have been blocked > by Microsoft servers. The SMTP response looks like this: > >> 5.7.1 Unfortunately, messages from [143.55.230.150] weren't sent. Please >> contact your Internet service provider since part of their network is on our >> block list (S3140). You can also refer your provider to >> http://mail.live.com/mail/troubleshooting.aspx#errors. [Name=Protocol Filter >> Agent][AGT=PFA][MxId=11BBF5965B0435E6] >> [DB1PEPF000509FE.eurprd03.prod.outlook.com >> <http://db1pepf000509fe.eurprd03.prod.outlook.com/> 2025-09-24T08:53:32.892Z >> 08DDFACB2E2D3F0D] > > Key details: > The issue has persisted for nearly a week. > Multiple support tickets were opened; each time the response was that the IPs > were mitigated, but bounces continued. > Follow-ups on those tickets have not brought progress. > The affected IPs are shared across many clients in different subpools. > Our internal analysis shows no drastic changes in volume or quality of > traffic. We've already taken proactive measures, but they have not resolved > the problem. > > At this point, we're hoping someone on this list might have a contact at > Microsoft or experience in escalating such cases that could help us get more > actionable feedback. > > Any help or guidance would be greatly appreciated. > > Thank you in advance, > Boris Pavlov > > > _______________________________________________ > mailop mailing list > [email protected] > https://list.mailop.org/listinfo/mailop -- The Delivery Expert Laura Atkins Word to the Wise [email protected] Delivery hints and commentary: http://www.wordtothewise.com/blog
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