TL;DR: In this paper, the authors revises the specifications in RFC 733, in order to serve the needs of the larger and more complex ARPA Internet Some of RFC733's features failed to gain adequate acceptance In order to simplify the standard and the software that follows it, these features have been removed and a different addressing scheme is used, to handle the case of internetwork mail.
Abstract: This document revises the specifications in RFC 733, in order to serve
the needs of the larger and more complex ARPA Internet Some of RFC
733's features failed to gain adequate acceptance In order to
simplify the standard and the software that follows it, these features
have been removed A different addressing scheme is used, to handle
the case of internetwork mail; and the concept of re-transmission has
been introduced Obsoletes RFC 733, NIC 41952