On Mon, 26 Jan 2026 at 15:08, David Landers via mailop <[email protected]> wrote:
> Possibly the S3150 block is an escalation of the below "temporarily rate > limited due to IP reputation" error? > I can confirm that we almost always see the S775 (451 4.7.650 – IP reputation) error for several days before the S3150 (550 5.7.1 – block list) error appears. In some cases, we are able to get the issue mitigated after one or two escalations via ticket. In other cases, we are unable to find any resolution and are forced to stop sending from those IPs for days. We are repeatedly advised to use JMRP and SNDS, but in our experience they are not helpful. We receive S3150 errors on IPs that have always been GREEN on SNDS and for which we have no FBL data at all. I also believe SNDS colors are unreliable and not correlated with inbox placement (despite the explanations on that site). We have not been able to establish any relationship between open rates and SNDS colors. Overall, it is extremely difficult to understand what Microsoft expects, what exactly their filters are flagging, and what actions we can realistically take to comply with their requirements. Additionally, the URLs referenced in the error messages often do not provide any explanation of the error—when they work at all. For example, http://mail.live.com/mail/troubleshooting.aspx#errors currently redirects to https://substrate.office.com/ip-domain-management-snds/postmaster/troubleshooting#errors, which returns a 500 error. At times, Microsoft’s filtering behavior appears "inconsistent" and does not seem to correlate with the traffic they are actually receiving. Stefano -- Stefano Bagnara Apache James/jDKIM/jSPF VOXmail/Mosaico.io/VoidLabs
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