I want to delete user but cannot add the same user again

[Riki YAMASHITA]

I've deleted user "IT Staff" with email address "g_it_new@..." and add it again. However it says that the account already exists. When I tried to sign in, it says that I do not have permission. 
What I want to do is:
> Completely delete the user and email address
> Add the same user again

[Nic Brough -Adaptavist-]

What user directory are you using?