Any idea on the approximate size of the mailout (e.g., total number of recipients)? If it's a lot compared to the regular daily outbound volume from your mail server(s) to HotMail.com's servers, then it's reasonable to assume that it was a sudden major spike in traffic from HotMail's perspective (this is where outbound rate limiting helps).
> 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 > >> > > > -- 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
