421.4.4.2 Connection Dropped

For a specific address, any messages being sent to them we are getting them held in queue and the last error is 421.4.2.2 connection dropped. I can ping the SMTP e-mail server fine and inbound/outbound e-mail is fine (mail is going in and out from our domain and receiving mail from external and internal senders).

What could cause this one person to drop our connection? Blacklist checks all come up clean.
pstiffsaeAsked:
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pstiffsaeAuthor Commented:
This was a confirmed issue on their end. Their e-mail server was rejecting a connection to all traffic.
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pstiffsaeAuthor Commented:
Additional error within the main screen of the queue is: 451.4.4.0 Primary IP responded with "421.4.4.2 Connection Dropped" Attempted failover to alternate host but that did not succeed. Either there are no alternative hosts or delivery failed to all alternative hosts.
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Tej Pratap Shukla ~DexterServer AdministratorCommented:
Hi...

This may happens due to following reasons: -

1). May be this is firewall issue

2). May be Your DNS MX records do not include the IP address of the sending server so when the recipient server does a lookup it does not find your server and rejects the email. If their mail servers are set to do a lookup first before accepting mail and you fail the lookup then they can be set to just drop you connection

3). May be You have been blacklisted or not whitelisted and therefore rejected. If you are on a blacklist that the recipient email systems uses then they may be configured to reject your email. The recipient mail system may use a white-list, if you are not on the white-list then the email is rejected.

Thanks
Dexter
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pstiffsaeAuthor Commented:
This was an issue on their end that was confirmed.
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