This is using MS SBS2011 exchange server. My user told me that he got the delayed mail delivery for mails attempted to send to few domains. The error message:
451 4.4.0 Primary target IP address responded with: "421 4.4.2, connection dropped due to socketerror. "attempted failover to alternate host, but that did not succeeded. Either there are no alternate host, or delivery failed to all hosted host.
Please advose
https://www.experts-exchange.com/questions/27918434/421-4-4-2-Connection-dropped-due-to-connection-reset.html