I've also seen Google provide this error when a domain had a spammer/phisher attempt to spoof said domain several hundred thousand times. Since Google saw their domain in the RFC5321.Mailfrom, even though the messages weren't authenticated and were rejected as per their DMARC policy, the domain's mere existence in the RFC5321.Mailfrom for SPF was enough to tank their reputation with Google to abysmal levels.
I'd suggest checking their DMARC reporting historical data (if available) to see if this potentially occurred recently. - Mark Alley Sent from mobile, please excuse any typos. On Wed, Apr 24, 2024, 5:09 AM Matus UHLAR - fantomas via mailop < mailop@mailop.org> wrote: > On 24.04.24 07:28, Simon Branch via mailop wrote: > > For the past 2 weeks, we have been unable to send mails to any gmail > users, > > nor any email domains hosted on Google's mail servers. We are using > > Microsoft 365. > > So I assume you send your mail through microsoft/outlook servers, you > can't > your outgoing IP, and don't need to change it. > > > Every time we attempt to send a message, we get the following > bounce-back: > > > > 550 5.7.350 Remote server returned message detected as spam -> 550 5.7.1 > [2a01:111:f403:261b::700 19] Gmail has detected that this message;is likely > suspicious due to the very low reputation of the sending;domain. > > To best protect our users from spam, the message has been;blocked. For > more information, go to; https://support.google.com/mail/answer/188131 > im8-20020a056214246800b00696b2e6b32asi14453219qvb.337 - gsmtp > > > > I have been in touch with Microsoft 365 support and they have double > > checked our SPF / DMARC / DKIM records and all are correct. > > > > The only advice Microsoft will give is to speak to Google. > > > > I have filled out one of Googles email cases, explaining that our DNS > > records are set up correctly and we are not spamming. > > > > Unfortunately, we have had no reply after a week. > > > > Is there anything we can do to help resolve the issue? > > I had similar problem with out customers' domain a few months ago. > The problem happened because of spamming from that domain (hijacked > account), while SPF and DKIM were correct. > > It took about month until mail started working. > > Make sure nobody did spam/mailbomb from your domain while having matching > SPF/DKIM. I guess that could include forwarding of spam messages or > creating mail loop etc. I also guess you signed into google postmaster > tools and configured your domain. > > https://postmaster.google.com/ > > check SPF/DKIM records if they don't allow sending authenticated mail from > other places. > > -- > Matus UHLAR - fantomas, uh...@fantomas.sk ; http://www.fantomas.sk/ > Warning: I wish NOT to receive e-mail advertising to this address. > Varovanie: na tuto adresu chcem NEDOSTAVAT akukolvek reklamnu postu. > Fighting for peace is like fucking for virginity... > _______________________________________________ > mailop mailing list > mailop@mailop.org > https://list.mailop.org/listinfo/mailop >
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