Active Directory domain name length

James used Ask the Experts™
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 . I need to build them a new internal active directory domain and was going to use but was wondering if a active directory domain name with 23 characters not including the int. or .com is to long ?
Watch Question

Do more with

Expert Office
EXPERT OFFICE® is a registered trademark of EXPERTS EXCHANGE®
Technology and Business Process Advisor
Most Valuable Expert 2013
It should be fine.  Just don't go beyond 15 in the netbios name (I STRONGLY recommend the netbios name be something VERY VERY SHORT - for example, if the company is "Twenty Three Characters Inc" then the internal NETBIOS name should be "TTC"
JamesSolutions Architect


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.

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
Shaun VermaakTechnical Specialist
Awarded 2017
Distinguished Expert 2018

You can probably then just add an shorter UPN, change it on users and sync

Do more with

Expert Office
Submit tech questions to Ask the Experts™ at any time to receive solutions, advice, and new ideas from leading industry professionals.

Start 7-Day Free Trial