Interesting. Your off-list reply to mine was bounced by Google (when our server relayed it). You wrote:
> The from header is: > edulink<at>bordengrammar.kent.sch.uk > however they've set a non-existent account as the reply to... Those look fine to me. But why was your message to me bounced by Google? Their bounce response reads: 'Our system has detected that this message is suspicious due to the nature of the content and/or the links within. To best protect our users from spam, the message has been blocked. Please visit https://support.google.com/mail/answer/188131 for more information.' You can read what Google say at that link. There is nothing in your email that looks at all like spam to me. Are you able to fix the DMARC entry in your DNS? It has spurious escaped quotes. On Sat, 12 Sep 2020 at 12:15, Dominic Raferd <domi...@timedicer.co.uk> wrote: > > On Fri, 11 Sep 2020 at 22:49, Julian Pilfold-Bagwell > <j...@bordengrammar.kent.sch.uk> wrote: > > > > I have a problem that's sprung to light after we bought in a 3rd party > > cloud provider. I have postfix 2.10 running on Centos 7 (main.cf below) > > and our 3rd party provider is relaying mail out via our server, using > > authentication on a legit account. However, the recipient ISPs reject > > mail with the error 554 5.7.1 recipient access denied, although this > > doesn't seem to happen on all the messages that are being sent. If > > we're sending say 60 messages, the first block of 20 will go through, > > the next 20 will be blocked and the final 20 will go through. I'm > > guessing that the receiving end is objecting to something in the headers > > from the relayed mail, but can't quite get to grips as to why it occurs > > in batches. > > > > The 3rd party provider is sending reports to all of our end users which > > is over a thousand emails+ so I've limited the delivery rate to 1 > > message per domain every twenty seconds to try to appear less spammy > > but it still happens as described. The error message is as below: > > > > NOQUEUE: reject: RCPT from smtp.overnetdata.com[5.153.65.228]: 554 5.7.1 > > <usern...@hotmail.com>: Recipient address rejected: Access denied; > > from=<edul...@bordengrammar.kent.sch.uk> to=<usern...@hotmail.com> > > proto=ESMTP helo=<www7> > > > > and we're receiving this from talktalk.co.uk, sky.com, yahoo.co.uk, > > hotmail.com, outlook.com and gmail.com sometimes talks to us, and > > sometimes doesn't. > > > > and main.cf is shown here:... > > The setup seems imperfect, and the version of postfix rather old, but > which if any of the imperfections is causing this new problem is hard > to say without fuller examples of what is being blocked, which I can > well understand you might not want to post on an open forum. My > observations are: > > Instead of 'smtp_use_tls = yes' it is advisable to use > 'smtp_tls_security_level = may' (Postfix 2.3+) > > Your SPF entry in DNS looks ok, provided as you say that the 3rd party > is sending your emails via your mail server and not independently. > Also your mail server's ip is not blacklisted at any of the 129 rbls I > regularly check, nor at https://ipremoval.sms.symantec.com/. You can > check its status with Microsoft by registering it at their Smart > Network Data Service. > > Your DMARC entry in DNS is broken, also you do not appear to be > signing outgoing emails with DKIM. But I doubt either of these is the > explanation for your problem. > > Is the third party sender using your domain in the 'From:' header as > well as in the envelope?
