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Have you confirmed your new External IP address with Logix, They may need to add it as an accepted address to allow mail in (as they wont be an open relay).
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MTA has given us USER ID and PASSWORD and dns name. So put only host address and user ID and password then it start working. Here we are putting right credentials but no luck.
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I have exchange server 2010 and we have set mail relay to logix. Means, our exchange send email to Logix and then logix forward email to repient domain. But today our exchange is not connecting with logix. earlier IP reputation was poor, so I changed the IP of exchange and same NAT in firewall. OWA is working fine using IP and DNS name. Again, I set relay to LOGIX, it &nbsp;is not connecting with exchange.<br />
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451 4.4.0 Primary target IP responded with: &quot;421 4.4.2 connection drop due to socket error. &quot;attemped failover to alternate host but that did not succeed. Either there are no alternate host or delivery failed to alternate host.&quot;
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I have exchange server 2010 and we have set mail relay to logix. Means, our exchange send email to Logix and then logix forward email to repient domain. But today our exchange is not connecting with logix. earlier IP reputation was poor, so I changed the IP of exchange and same NAT in firewall. OWA is working fine using IP and DNS name. Again, I set relay to LOGIX, it  is not connecting with exchange.

451 4.4.0 Primary target IP responded with: "421 4.4.2 connection drop due to socket error. "attemped failover to alternate host but that did not succeed. Either there are no alternate host or delivery failed to alternate host."

Exchange is not connecting with MT service provider

Exchange is the server side of a collaborative application product that is part of the Microsoft Server infrastructure. Exchange's major features include email, calendaring, contacts and tasks, support for mobile and web-based access to information, and support for data storage.

Exchange

The Domain Name System (DNS) is a hierarchical, globally distributed system responsible for associating the name of a computer, service or other resource into an IP address for connecting to the Internet or a private network. Most prominently, it translates domain names to the numerical IP addresses needed for the purpose of computer services and devices worldwide.