Employee is getting NDR when sending to one company. Her email works fine to other companies. Message Tracking shows 451 <FrontEndExchangeServer.domain.com> is invalid or DNS says does not exist. Their ServerIp and ServerHostname matches with the test we did with mxtoolbox. The recipient was able to receive a test email from a test hotmail account.
Using is seeing in NDR
#550 4.4.7 QUEUE.Expired;
message expired ##