Connected to but sender was rejected. Remote host said: 451 4.4.0 DNS temporary failure


we are trying to email using the Mail Relay.

we are getting a bounced message:

"Connected to but sender was rejected.
Remote host said: 451 4.4.0 DNS temporary failure (chkuser) I'm not going to try again; this message has been in the queue too long."

The following is the tracert from my side;

C:\Documents and Settings\Administrator>tracert

Tracing route to []
over a maximum of 30 hops:

  1    <1 ms    <1 ms    <1 ms []
  2     6 ms     5 ms     7 ms
  3     7 ms     *        8 ms []
  4     8 ms    27 ms     7 ms []
  5     6 ms     7 ms     7 ms []
  6    48 ms    52 ms    47 ms []
  7    48 ms    55 ms    47 ms []
  8    48 ms    49 ms    68 ms []
  9    50 ms    38 ms    37 ms []
 10    40 ms    37 ms    35 ms []
 11    37 ms    45 ms    35 ms []
 12    41 ms    40 ms    35 ms []
 13    38 ms    35 ms    36 ms []
 14     *        *        *     Request timed out.
 15     *        *        *     Request timed out.
 16     *    

Would it be correct to say that their is a problem connecting to them after [] - i.e one of their internal servers / routing or a firewall or some rule is a problem?

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LeeDerbyshireConnect With a Mentor Commented:
Actually, it doesn't matter that they're not the same, but they often are.  I was suggesting that they might be your best point of contact for DNS issues.

This organization might do more DNS checking than most.  Some admins enforce rigorous domain DNS checking to combat spam.  The obvious risk is that they will lose some valid emails without even knowing about it.
Try your own IP address here, and see if you're on any blacklists:
meluAuthor Commented:
Seems fine. We are not blacklisted.

Also please see the results of the telnet:

C:\Documents and Settings\Administrator>telnet 25

mail from : <>
451 4.4.0 DNS temporary failure (chkuser)
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My telnet from here returned OK .  Try a DNS Report test on your domain name here;
meluAuthor Commented:
Can you please see the report

For security reasons - I dont want to reveal the domain name [here].

I would guess that the 'Mail server host name in greeting' warning is the most significant here.  Have a look at the properties of your Default SMTP Virtual Server, and enter the name '' as the Fully-Qualified Domain Name.
meluAuthor Commented:

I have corrected the 'Mail server host name in greeting' warning.

I am still not able to resolve that error. Any idea what could be causing the problem?


Well, that seemed the most obvious to me, but I guess it's time to work through the other failed items.  The error message
451 4.4.0 DNS temporary failure (chkuser)
does seem to suggest a DNS problem, and you had a lot more fails and warnings than I would have expected.  Trouble is, I don't know what most of them mean, and I think only your ISP (assuming they are your DNS provider) can fix them.
meluAuthor Commented:
Interesting thought.

The ISP is - and the DNS provider is upscalehost

They are not the same.

But, we dont have any problems sending to anyone else apart from this one organisation
meluAuthor Commented:
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