I'll try to be brief and can provide more info if needed.
I'm doing an on-premise migration from ex2010(sbs server) to ex2016. I'm following the technet doc that has done a pretty good job for me in the past. I've completed all the steps and am ready to actually move mailboxes.
My issue is:
When i point the firewall port 25 to the NEW ex2016, mail is not delivered to mailboxes still on the ex2010 server.
I've made all of the internal uri's match the external fqdn's; I've pointed autodiscover to the correct fqdn. I've changed the connection point and configured outlookanywhere; All of my internal DNS records for the fqdn mail.domain.com are pointing to the new ex2016 server. I believe the 2 servers are communicating as OWA connects to the old server/interface for mailboxes on the old server. I acutally migrated the admin mailbox, and OWA give me the interface for the ex2016 server. All outbound mail works. With port 25 pointing to the OLD server, all inbound works for mailboxes on old server, a migrated mailbox on new server, and a freshly created mailbox on new server.
I guess i could leave the firewall pointed to the old server and migrate mailboxes as that seems to work well...but it just seems like something is not quite right here and i don't want to compound the issue unneededly.
thoughts appreciated and thanks in advance,
8/22/2022 - Mon
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