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Active Directory domain name length

I have a customer that has a external domain name which is 23 characters long that they want to use for a new office 365 tenant so as an example domain looks like this 23characters.com . I need to build them a new internal active directory domain and was going to use int.23characters.com but was wondering if a active directory domain name with 23 characters not including the int. or .com is to long ?
Microsoft 365Active Directory

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Shaun Vermaak
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Lee W, MVP
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Great, thanks for that. The company name is 3 words so I can make the netbios name 3 characters to keep it short.

I was thinking of shortening the internal AD name but i thought it was best practice to have the internal AD domain a sub-domain of the external.
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Sajid Shaik M
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onpremise domain and azure ad are different things... you can create a domain and sync users ... it sync only UPN and Password which authenticates at office 365 by azure ad..

for detailed guidiance please check the following


all the best
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Shaun Vermaak
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You can probably then just add an shorter UPN, change it on users and sync
Active Directory
Active Directory

Active Directory (AD) is a Microsoft brand for identity-related capabilities. In the on-premises world, Windows Server AD provides a set of identity capabilities and services, and is hugely popular (88% of Fortune 1000 and 95% of enterprises use AD). This topic includes all things Active Directory including DNS, Group Policy, DFS, troubleshooting, ADFS, and all other topics under the Microsoft AD and identity umbrella.

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