You have several ways to achieve this goal:

• Native, if you assign the department to andrea@freshservice.com automatically the department field of the ticket will be populated with the department associated with the requester.
• If, for example, the requester is associated with multiple departments you can use the api Update Ticket PUT, domain.freshservice.com/api/v2/tickets/ticket id numeric with this payload: 

{

"department_id": id_department

}

• You can use properties of the requester and not the email to avoid making hundreds of conditions. For example if the job title field contains "Finance" then set department as Finance.
• You can use custom objects with emails or other requester properties and map them to departments. For example: Read from Custom Object if requester is requester then set department as Department (requester and department are the two columns of the custom object)

Let me know if I understand the requirement
Have a good evening