Recently, emails from our server to @ntlworld.com addresseses are being blocked and the NDR from Virgin Media states "... Temporary SMC Policy Violation detected ..."
I've posted a sample below.
These emails are all messages to confirmed opt-in subscribers of email discussion-lists hosted on our server. We do not send spam and we have various filters in place to block spam from reaching these lists. We publish SPF and DMARC records and DKIM sign our outgoing mail.
Cisco reports our IP as having a good email reputation with zero spam and not listed on any legitimate blacklists.
It's not clear what "SMC Policy Violation" means, but any assistance in getting this block removed would be greatly appreciated.
Thanks.
Nov 6 21:17:13 lhr postfix/smtp[27647]: 40BCA25A79: to=<REDACTED@ntlworld.com>, relay=mx.tb.ukmail.iss.as9143.net[212.54.56.11]:25, delay=1025, delays=1024/0.02/0.19/0.61, dsn=4.2.0, status=deferred (host mx.tb.ukmail.iss.as9143.net[212.54.56.11] said: 421 4.2.0 MXIN618 Temporary SMC Policy Violation detected, retry later ;id=jT3pmUDGknQyPjT3pmYK4X;sid=jT3pmUDGknQyP;mta=mx7.tb;dt=2021-11-06T22:17:13+01:00;ipsrc=178.62.98.103; (in reply to end of DATA command))