box number

noun1

1. •
   A numerical address for postal correspondence, managed by a company or organisation on behalf of the addressee, and used e.g. for convenience, if one does not have a suitable physical address for receiving mail, or to avoid giving one's real address (e.g. in a newspaper advertisement).

   • They didn't give me a proper address, only a box number.
   • Would anyone with knowledge of the present whereabouts of Mrs Doris Miggins, formerly of Station Road, please contact Box No. 99, Puddletown Evening Gazette.