You can also add requesters by importing from CSV files. To import requesters from CSV file
Below are the conditions followed in CSV Import.
1. Login name, email, and domain will be used as parameters to decide if a user already exists or not.
2. If a user is matched based on email but without login, the user will be updated and login will be given
3. If a user is not found based on the provided details, a new user with login will be added during import.
4. In an import both add and update cases are possible, hence the login name and password mandatory.
5. In case of update, we won't update the password for existing users with login,
In regards to the 1st point, user matched based on email is based on configuration under Admin>Self Service Portal>