Sep 15 2021
Are problems to be expected when integrating / linking an existing domain into the O365 account regarding email addresses that did not receive an O365 user and an O365 license?
Will the email traffic for such users continue to function as usual or does something have to be taken into account so that the functionality can be guaranteed?
Is there also an interruption to be expected when linking the existing domain to the O365 account?
Can emails be "lost" in the event of such an interruption?
Sep 19 2021
This process is very straight forward these days. No outage or data loss should happen if domain is added correctly. Make sure you add publish your DNS records and follow the instructions from the link below.
Add a domain to Microsoft 365 - Microsoft 365 admin | Microsoft Docs