On 3/17/2021 9:33 PM, Vaibhav via mailop wrote:
Hi,

We're an ESP sending emails on behalf of clients who are receiving the following bounce error from virgin media domains (blueyonder.co.uk <http://blueyonder.co.uk>, ntlworld.com <http://ntlworld.com>, virginmedia.com <http://virginmedia.com>) across multiple different domains and IPs:

SMTP Error : *421 4.2.0 MXIN618 Temporary SMC Policy Violation detected, retry later ;id=MVLFlm4kdboSoMVLGlk2I5;sid=MVLFlm4kdboSo;mta=mx1.tb;dt=2021-03-17T13:32:03+01:00*
*
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We have tried "sending later", as suggested in the error but no emails are being allowed through. Would someone please be able to help me with the cause of this error, and how we may resolve it moving forwards? I can't find any information on it online nor action I can take for it to be removed

It's their sender mail compliance or something like that.  Your systems are likely being blocked for sending spam / user complaints.  See https://netreport.virginmedia.com/netreport/ for more info but I don't know how to reach their postmaster.  They have a community forum linked there as well.

Have you looked at the postmaster hygiene of your customers?  Any of them using things like bought lists?  What's your ESP?

Regards,

KAM

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