The X.400 series protocols have been defined by CCITT to provide an Interpersonal Messaging Service (IPMS), making use of a store and forward Message Transfer Service. It is expected that this standard will be implemented very widely. This document describes a set of mappings which will enable interworking between systems operating the X.400 protocols and systems using RFC-822 mail protocol or protocols derived from RFC-822. This RFC suggests a proposed protocol for the ARPA-Internet community, and requests discussion and suggestions for improvements.