Hi, @Vladimir Kiesner Following two options are available: - Rename - Migrate However, either of the above has to performed on premises. Then, sync using Ad Connect. However, renaming can see unforeseen issues. Please refer this. Ideally, try this first in Test env and monitor for sometime to see if anything breaks. Things that could break are 3rd party apps, older versions of exchange, etc.
Azure AD connect - add second domain with same NetBios name (different forests, FQDNs)

hello. Currently we have our domain synced to Azure AD. We want to sync second domain into same tenant. Problem is - we have same NETBIOS domain name. Is it a problem?
To clarify:
Forest1/Domain1: fish.lv synced to Azure -> fish.onmicrosoft.com, internal domain fish.lv, domain name pre-Windows 2000: fish
Forest2/Domain 2: fish.lt need to be synced to same tenant -> fish.onmicrosoft.com, internal domain fish.lt, domain name pre-Windows 2000: fish
As far as i know, in general such configuration is supported (two forests|domains, one Azure AD connect server), BUT: having same legacy domain name is gray area for me. I know, what we are unable to make domain trust because of that.