How to delete the rejestered mail id's?

How to delete the rejestered mail id's?

Hi i am the admin of my domain protouchinterior.com in Zoho. When i try to create a email id for my colleage ,it shows that the mail id already exists but i am unable to find it the users in the control panel.

the email id i am trying to add: - devadas@protouchinterior.com

Regards
Anish Mohan