In our experience, the majors are very quick to pull the trigger on throttling smaller ESPs.
This is what we do; it's Postfix-specific as we host/service Zimbra systems exclusively: https://www.missioncriticalemail.com/2021/06/03/zimbra-selective-postfix-rate-limiting-to-improve-email-deliverability/ Hope that helps, Mark -- _________________________________________________________________ L. Mark Stone, Founder North America's Leading Zimbra VAR/BSP/Training Partner For Companies With Mission-Critical Email Needs Winner of the Zimbra Americas VAR Partner of the Year - Two Years Running ! ----- Original Message ----- | From: "Boris Pavlov via mailop" <[email protected]> | To: "Laura Atkins" <[email protected]> | Cc: [email protected] | Sent: Wednesday, September 24, 2025 7:51:52 AM | Subject: Re: [mailop] Request for assistance with Microsoft IP blocklist issue of over 40 IPs | Hello Laura, | Thank you for your response. We will try that although there have not been any | changes in our MTA configuration or serious fluctuations of volume being sent | to Microsoft. | Appreciate your help, | Boris Pavlov | On Wed, Sep 24, 2025 at 1:02 PM Laura Atkins < [ mailto:[email protected] | | [email protected] ] > wrote: || 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 < [ mailto:[email protected] | ||| [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 | |||| http://mail.live.com/mail/troubleshooting.aspx#errors ] . [Name=Protocol Filter |||| Agent][AGT=PFA][MxId=11BBF5965B0435E6] [ [ |||| http://db1pepf000509fe.eurprd03.prod.outlook.com/ | |||| 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 ||| [ mailto:[email protected] | [email protected] ] ||| [ https://list.mailop.org/listinfo/mailop | ||| https://list.mailop.org/listinfo/mailop ] || -- || The Delivery Expert || Laura Atkins || Word to the Wise || [ mailto:[email protected] | [email protected] ] || Delivery hints and commentary: [ http://www.wordtothewise.com/blog | || http://www.wordtothewise.com/blog ] | _______________________________________________ | mailop mailing list | [email protected] | https://list.mailop.org/listinfo/mailop _______________________________________________ mailop mailing list [email protected] https://list.mailop.org/listinfo/mailop
