Exchange queue 451 4.4.0 Primary target IP address responded with: "235 00000...

You might find messages staying in queue on your email server (mixed environment 2007/2010 Exchange) and Error showing:

451 4.4.0 Primary target IP address responded with: "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." Attempted failover to alternate host, but that did not succeed. Either there are no alternate hosts, or delivery failed to all alternate hosts.

  • Check DNS connectivity
  • Check network
  • Check services
  • Open Send connector and check if the server is in source servers list
  • Check O365 connector (if your are trying to send mail from your on-premise environment to O365 user (name on certificate setting or IP setting)

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