email not sending to a specific domain

We have an Exchange 2010 server running on SBS2011. there is one specific domain we are not able to email. looking at the message queue it just sits in a Connecting or Retry status. Eventually getting an NDR message.

I ran nslookup -type=mx domainame and it resolves. I try to telnet and it gives me an error 421 4.3.2 system not accepting network messages... connection host lost

I have verified that GFI (Spam Solution) has the domain in the allow list.
350ztnAsked:
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350ztnAuthor Commented:
i was able to resolve the issue. found out the isp was on blacklist
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Seth SimmonsSr. Systems AdministratorCommented:
sounds like the issue is on their side considering a) it is one specific domain and b) your telnet test fails
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Simon Butler (Sembee)ConsultantCommented:
Have you tried any of the public tools, like those at mxtoolbox, to see if the problem is widespread.
If those tools fail as well, then the problem is not yours.
If they are successful, then it could be that they have blacklisted you. Not a lot you can do without the other side assisting though.

Simon.
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350ztnAuthor Commented:
are there any other tests that I can run to ensure the problem does not lie within my network? I have checked the mxtoolbox and both my domain and the recipient domain test correctly, no errors. the only thing that I did see was when I run the microsoft remote connectivity wizard and select the smtp outbound. I test my domain and their domain and both are on a blacklist ABHL...but that is no longer managed and I can not make a request to remove my domain nor their domain from that list. mxtoolbox blacklsit check doesnt show either domain on a blacklist?
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