 Occasionally, because of political instability when a post office could not provide normal services, incoming mail from a mail steamer would be delivered to a local delivery service, which would deliver the mail and charge the addressee an extra fee for the service.When this occurred, the local delivery service would place its own local service stamp or mark on the envelope when the extra fee was paid.Mail carried by these steamers – sometimes known as paquebot mail – was subject to various regulations by the governments involved as well as the Universal Postal Union's (UPU) regulations stated at the UPU Vienna Conference of 1891.