I'm in the middle of an Exchange 2003 / 2007 to 2010 transition. Mailflow was working between all 3 environments. I installed an Exchange 2010 Edge Transport server in the DMZ, created a new subscription and applied to internal org via Hub Transport 2010 server. Test-EdgeSynchronization and Start-Syncrhonization were successful but mail starts queuing up on the Hub transport server with error 451 4.4.0 and 451 5.7.3 Cannot achieve Exchange Server authentication.
Any ideas what may be wrong?