Is there a limit to register user mail box on NT(OS)

Hello Everyone.I have one question about domino capacity on between AIX and NT.

When both AIX and NT OS have same tpmc, same spec, Is only there some limit to regist user mail on NT Machine(for example : AIX can register 1000 user, but NT can’t register 1000 user)? Some engineer tell me about this, so i wanna know correct answer about that.

Please let me know if you have good idea.

Thanks.