This paper describes the implementation of PMDF, a portable Pascal-based internetwork mail router. It includes features such as aliasing, forwarding, queueing automatic routing to network gateways, message batching and message retransmission and is currently being used as a gateway between the Computer Science Network's PhoneNet and local electronic mail systems. PMDF is unique among internetwork mailers in that it is portable. All operating system dependent functions have been isolated to one module and therefore PMDF can be ported to any system that has a Pascal compiler and provides the functions necessary to implement the operating system dependent module.