DNS Suffix , Internal DNS zones, External DNS (M365_UCTechiLab#5) - AD and Exchange 2016
Access the AD Server and DNS and Create new DNS Zone.
I would suggest to fix the it/DNS suffix add then you can verify by accessing the ADUC and create user
For DNS work in the Exchange and also AADConnect to verify UPNSuffix we should have domain in the both side of the ADs. AAD will have the automatically when we verify part of the tenant verification by adding a CNAME in public domain where you have domain records. Addition to that if you dont have this in AD DNS (On-Prem) then you will required to add.
Follow the steps and it will be straight forward in new environment and if you already using this domain in your exchange then this wont be a problem or not required to create.
Go to Active Directory Server (AD) > AD Domains and Trusts
Right click on top Active Directory Domains and Trust > UPN Suffixes and Add the UPN you required
for DNS zone we will be creating new zone under this name
Add the domain you which you created in the DNS Suffix
Do not allow dynamic updates
Adding Exchange A records on all new zones