1506: A Tutorial on Gatewaying between X.400 and Internet Mail.

There are many ways in which X.400 and Internet (STD 11, RFC 822) mail systems can be interconnected. Addresses and service elements can be mapped onto each other in different ways. From the early available gateway implementations, one was not necessarily better than another, but the sole fact that each handled the mappings in a different way led to major interworking problems, especially when a message (or address) crossed more than one gateway. The need for one global standard on how to implement X.400 - Internet mail gatewaying was satisfied by the Internet Request For Comments 1327, titled "Mapping between X.400(1988)/ISO 10021 and RFC 822."