A correspondent writes: “…is there no translation for the expression “PO Box” you can use in your address?”

Indeed, we use Jèrriais addresses as a matter of course. We list our Department’s PO Box number in English as a reasonable compromise for ease of communication. But we could always use:
Boête Postale
or
Bosc à la Poste
(B.P.)

So, feel free to Jèrrify “PO Box” if you’re writing to us!

More postal vocab here.