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I'm trying to send an email to M@Danielmadison.co.uk (there are no attachments being sent if that would affect anything) and i keep getting the following message: Delivery to the following recipient failed permanently:

 M@danielmadison.co.uk

Technical details of permanent failure: Google tried to deliver your message, but it was rejected by the server for the recipient domain danielmadison.co.uk by mxcluster1.one.com. [91.198.169.8].

The error that the other server returned was: 554 5.7.1 : Recipient address rejected: Unknown recipient"

This is coming from the email address: mailer-daemon@googlemail.com

I am also sending my emails to the domain via GMail. I've been trying for several days now, and I have no clue what to do, if I'm honest. Would really appreciate some help

Qreq
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The problem here is that the recipient mail server is blatantly lying. It's sent an SMTP error code 554 5.7.1 that means it is refusing to relay mail, but in the human readable text, it states "Unknown recipient". Both cannot be the cause of the failure. Someone has deliberately configured the mail server to confuse and mislead.

In the case of the mail server refusing to relay, the problem is that the recipient's mail server is misconfigured; it has an MX record for the domain pointed to it, so it should be accepting mail for that domain. Not doing so indicates that it is misconfigured.

Further, blatantly sending back wrong error messages is confusing and leads to the loss of legitimate mail in the best case.

Your recipient needs to get their email service fixed. Until it is fixed, you'll need to find another way to contact them.

Michael Hampton
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  • This answer confuse me, because normally both refusing to relay and a non-existent recipient is reported with code `550`. But you seem to suggest those are two different codes. It would probably be less confusing, if you mentioned the numbers of the error codes in your answer. – kasperd Apr 22 '16 at 17:26
  • @kasperd 550 5.1.1 means unknown recipient. 554 5.7.1 means relaying denied. – Michael Hampton Apr 22 '16 at 19:34
  • I have not come across any mail server using `554` when refusing to relay. They have all been using `550`. – kasperd Apr 22 '16 at 19:39
  • Where are you finding these servers? I've never seen such a configuration. – Michael Hampton Apr 22 '16 at 19:42
  • As an example consider the mail server used by `stackoverflow.com`. The first priority MX is named `aspmx.l.google.com`. So I type commands: `telnet aspmx.l.google.com. 25`, `HELO localhost`, `MAIL From:<>`, `RCPT To:`, and I get code `550`. – kasperd Apr 23 '16 at 12:15
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    @kasperd Google overall has a pretty cavalier attitude toward RFCs, so I'm not sure that's the best example. – Michael Hampton Apr 23 '16 at 15:51
  • I see that behavior from every single mail server I have tested. – kasperd Apr 23 '16 at 20:27
  • @kasperd I looked at Gmail's response, and it doesn't seem that you viewed the entire response. It begins... `550-5.1.1 The email account that you tried to reach does not exist.` Which, while not the ideal response, is perfectly valid, and corresponds to what I said above. A local postfix server returns: `554 5.7.1 : Relay access denied` which is also correct. – Michael Hampton Apr 23 '16 at 20:47
  • You said the error code to use for this is `554`, and you implied that the majority of mail servers respond with `554` under those circumstances. Can you name any server that actually uses `554`? I have never seen it. I have only seen `550` being used. – kasperd Apr 23 '16 at 20:52
  • `hotmail.com` responds with `550`. Exim in a standard configuration responds with `550`. I also checked the mail server for `worldwidewords.org`, which also responds with `550`. I have yet to see a server responding with `554` when refusing to relay. – kasperd Apr 23 '16 at 20:58
  • @kasperd You keep omitting the extended status code and associated text. Without them, your statements are utterly irrelevant to either this question or answer. – Michael Hampton Apr 23 '16 at 21:17
  • The extended status codes are optional. And I only saw extended status codes from gmail. None of the other servers I tested would send any extended status codes. Besides, I was only saying something about the basic status codes, not the extended ones. – kasperd Apr 23 '16 at 21:26
  • I hate to say it, but I see the same sort of thing on my fairly bog-standard sendmail 8.14.4 on CentOS 6: `550 5.7.1 ... Relaying denied. Proper authentication required`. Though still +1 for the answer, because Google really does play by their own rules, so you pretty much can't discover what the problem is by following them. – MadHatter Apr 25 '16 at 07:26