Just to add that the Ip were not listed in any rbl, and the message I think was responsible was an invitation for an event in September.
Traffic numbers were standard. Just this user that really messed up using a completely wrong mailing list.... Il Mer 5 Ago 2026, 20:29 hg user <[email protected]> ha scritto: > I have been blocked for about 26 hours with S775 error and the problem I > identified was of a sender with too many wrong addressed. I'm not even sure > about it, still put the events in order. > From that moment both IPs (working as MTA for one domain for more than 15 > years, perhaps 20+) were "rate limited" but actually no message could be > sent by any sender. > > I created a new mta with a brand new, cold ip, whose configuration was > also missing reverse ip, and tunnelled messages were delivered. Can't say > if they went to inbox spam or junk... > > Support also replied, unexpectedly, but 2 hours after the ban was lifted > so they found nothing wrong. > > > Il Mer 5 Ago 2026, 20:22 Randolf Richardson, Postmaster via mailop < > [email protected]> ha scritto: > >> You should look into the message content to make sure that it >> isn't >> including any links to phishing web sites, web sites that are known >> to distribute malicious software, MLM/pyramid-scheme affiliate links, >> etc. There are certain subject lines that can get people into >> trouble as well, and then there are compliance issues with sending >> out bulk messages that should to be included in the SMTP headers. >> >> Also, you should check all of your eMail server IP addresses >> (IPv4 >> and IPv6) for inclusion in blacklists: >> >> https://multirbl.valli.org/ >> >> In the meantime, rate-limiting outbound eMails for your clients >> will >> also help. Do you have a rough estimate of the total number of >> recipients? Also, were the messages sent separate to each recipient, >> or were multiple recipients grouped together? >> >> > Hi, >> > yesterday due to a user sending a newsletter to a list recipients full >> of >> > errors (I'm sure about this, I don't know what the message text was) >> > Microsoft started to "temporarily" rate limiting my 2 sending IPs. >> > >> > The messages are refused with the following log: >> > 451 4.7.650 The mail server [.....] has been temporarily rate limited >> due >> > to IP reputation. For e-mail delivery information, see >> > https://aka.ms/postmaster (S775) [Name=Protocol Filter Agent][AGT=PFA] >> > >> > I registered to SNDS and found that these IPs turned red yesterday. I >> > opened a ticket and the first automatic reply was that the IPs "do not >> > qualify for mitigation". >> > >> > As requested, I then replied with a detailed email trying to explain the >> > situation but reading previous posts it seems that they won't follow up. >> > >> > So I ask you: >> > - did you have a S775 block in the past and how long was it ? >> > - will I ever receive an answer from MS or my only possibility is >> checking >> > the logs ? >> > >> > I have a brand new server with another public IP that is part of our AS >> and >> > listed in SPF. I may route traffic to hotmail via this server but the >> IP is >> > "cold". I read that someone solved this way but it was not clear if the >> new >> > Ip was already warmed. >> > >> > Thank you >> > >> >> >> -- >> Postmaster - [email protected] >> Randolf Richardson, CNA - [email protected] >> Inter-Corporate Computer & Network Services, Inc. >> Vancouver, Beautiful British Columbia, Canada >> https://www.inter-corporate.com/ >> >> >> _______________________________________________ >> mailop mailing list >> [email protected] >> https://list.mailop.org/listinfo/mailop >> >
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