After setting up the new exchange server 2016 as a upgrade to the existing exchange server 2010 it looks as if it was success.
Using the owa web outlook I am able to send and receive emails internally and externally as well as work with all the other functions (this includes old user mailboxes as well as migrated and newly created mailboxes).
Unfortunately when I try to connect using outlook 2016 the process detects the logged in AD user correctly, but it will not accept the login credentials (I tried different users, different login options firstname.lastname@example.org or domain\user with out any luck).
I check all the DNS configurations for autodiscover and MX records and restarted the server. Unfortunately that didn't help.
There is no AV installed on servers and no firewall or VLAN between the client computer.
I am able to configure the outlook 2016 if I am connecting externally or on local LAN if I disable MAPI in registry on the client computer.
The disabled MAPI in registry allows me to use the migrated user mailbox in outlook 2016, except not without requesting to enter user credentials which will fail. Outlook will continue to function normal if I cancel the login request.
Testing outlook connectivity on exchange server 2016 using "Test-OutlookConnectity" is successful after I adjusted LmcompatibilityLevel to 2 in registry and group policy.
Are there any other ideas on what else could be the problem?
here are some of the links I used to troubleshoot: