How To Create an Admin Account
This will create an additional admin account with the password of 'test123':
zmprov ca firstname.lastname@example.org test123 zimbraIsAdminAccount TRUE
This will transform a normal existed user account into an admin account (in this example futur-admin will become an admin) :
zmprov ma email@example.com zimbraIsAdminAccount TRUE
To change the password run:
zmprov sp firstname.lastname@example.org NEW_PASSWORD
The admin account email@example.com was created during installation.