I suggest you try to avoid using open textfield for the Postcode. Then you can use 2 dependent fields. The first field will be the select of employees number range. The second will be one of postcode selects, depending on the first choice. Then you can use the standard functionality: using select field key as the email.
If for a fixed employee number range you have individual emails for different postcode values then it is straitforward.
If not, still you can do it if all postcode values could be grouped into ranges, so that each range gets its own email (define select values for postcode ranges same as you did for employees number).