Any assistance is need

Any assistance is need

I have attempted to add email user b.vimal@shenbagahotel.com  as a regular mail user with b.arun  @shenbagahotel.com  and get an error saying the user already exists, but it does not show on the list. I have already confirmed it is not the secondary account for the super user.  I simply need to b.vimal@shenbagahotel.com   under the above super account.    Any assistance is appreciated. thank you.