Use the following steps to allow a company level to use the same email to login into ESS:
Step 1: Change the company level user's email address on their user profile to a fictitious email address by adding a numeric/s or special character.
Navigate > Configuration > Security > Security > User Profiles
Step 2: Insert the correct email address on the company level user's employee record.
Navigate > Employee > Basic Information > Basic Profile > Contact Details
Step 4: Search for the ESS registered email under the Employee User List filter on the user screen, and change the status from employee to company and give the user their required company level permissions.
Navigate > Configuration > Security > Security > User Profiles