In the process of migrating from Exchange 2010 to Exchange 2016.
Currently Exchange 2010 is the Mailbox, Hub Transport, and Client Access server. Exchange 2016 is only a Mailbox server.
I want to verify mailflow between the 2 Exchange servers and currently it isn't working.
Current environment is like this:
Internet --> Sonicwall Email Security Virtual Appliance (spam smarthost) --> Exchange 2010
Exchange 2010 is working fine to send and receive emails that are external or mailboxes stored on its database.
However I cannot get Exchange 2016 to send emails externally (outside of the domain) or send emails internally (to mailboxes either on Exchange 2010 or Exchange 2016).
I checked the Message Tracking logs on Exchange 2016 and I see this error:
S:ItemEntryId=00-00-00-00-4F-AE-F9-BB-EF-20-ED-4B-B0-C6-7C-88-01-33-D1-DB-07-00-EE-FA-5A-AE-64-B2-A9-47-93-F1-13-72-CF-E6-C7-EF-00-00-00-00-01-0F-00-00-EE-FA-5A-AE-64-B2-A9-47-93-F1-13-72-CF-E6-C7-EF-00-00-00-00-19-F0-00-00;'S:DiagnosticInfo=Error: RetrySmtp, Diagnostic Information: Stage:UpdateMsgIdToPoisonContextMapping, SmtpResponse:451 4.4.0 DNS query failed. The error was: SMTPSEND.DNS.NonExistentDomain; nonexistent domain mailboxtransportsubmissioninternalproxy -> DnsDomainDoesNotExist: InfoDomainNonexistent, details:FailedRecipientCount:0; RetryRecipientCount:0';S:DeliveryPriority=Normal
I am not sure why Exchange 2016 cannot resolve the internal domain or external domains. In the IPv4 settings in the network adaptor the DNS settings are set to our domain controller and I am able to resolve and ping each Exchange server to/from each other so they are able to resolve and see each other on the network.
What other things should I be looking at to find out what's going on with the mailflow?