I have a really urgent issue that I've wasted days going in the wrong direction trying to troubleshoot and now need some help please experts!
Many messages sent through my exchange server are sitting in the outbound queue with the error
451 4.4.0 Primary target IP address responded with "421 please try again later" attempted to failover to alternate host but that did not succeed.
I have googled this error, but the resulting posts are too complicated for me to follow without risking breaking my server completely.
Would some kind soul please talk me through fixing this issue.