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451-4.4.0 Primary Target IP Responded With ESMTP Service Not Available

Hi Guys

One of my clients has an issue being unable to send to a specific email address, they are running SBS 2008 and each time they attempt to send an email to address in the question, the message sits in the exchange queue and fails to send. I looked in Exchange Message Console and can see the following error is listed against the relevant queue "451-4.4.0 Primary Target IP Responded with: "554-gmx.net (mxgmx002) Nemesis ESMTP Service Not Available"

I have tested sending mail from my account and the recipient receives the email without any issues.

Any Ideas?
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Daniel Bertolone
Asked:
Daniel Bertolone
1 Solution
 
KimputerCommented:
Usually, it's because the OTHER side is doing some checks on the connection.
Please check if the public IP on the SBS 2008 has a correct PTR record (nslookup IPnr should return a valid hostname).
Other things could be your IP address is blacklisted somehow (check with https://mxtoolbox.com/blacklists.aspx)
Also check you're talking to the correct server (DNS problem).
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skullnobrainsCommented:
agreed

additionally performing a dns lookup on the valid hostname returned by the PTR query should return the inital IP address
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Daniel BertoloneAuthor Commented:
PTR record was the cause
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