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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