My last Resource :
History : We migrated our exchange 2007 to 2010. We have one main site(Site AA) and one remote site(Site B). Consultant hand over us main site with exchange 2010 and remotesite with exchage 2010.
Primary role server on AA site was migrated. While B site mail were still going thorough old exchange. We been advise that when we ready sipmly turn off the old server and reboot all other server it will be fine. However , when we did they B site users were not able to send email on AA site. They can send & receiver external, they can receive internal but not able to send internally on site AA.
We notice that message are queue on B site with error "451 4.4.0 & 451 5.7.3 Cannot Achieve Exchange Server Authentication" . We tuned on old server to make it like normal but still same issue .. B site server fording message to old site but old site not forwarfing to AA site Error : 451 4.4.0 & 451 5.7.3 Cannot Achieve Exchange Server Authentication
Please help.. happy to add require logs