There are over 2500 RFC's. Each RFC is known by a number. For instance, RFC 1180 presents a tutorial on TCP/IP, RFC 1920 lists the current standards RFC's and explains the RFC standards process, and RFC 1941 is a FAQ list on the topic of Internet deployment in educational establishments.
MX record. A mail exchanger record (MX record) is a type of resource record in the Domain Name System that specifies a mail server responsible for accepting email messages on behalf of a recipient's domain, and a preference value used to prioritize mail delivery if multiple mail servers are available.
LGM-118 Peacekeeper. The LGM-118 Peacekeeper, also known as the MX missile (for Missile-eXperimental), was a land-based ICBM deployed by the United States starting in 1986. The Peacekeeper was a MIRV missile that could carry up to 10 re-entry vehicles, each armed with a 300-kiloton W87 warhead in a Mk.21 reentry vehicle (RV).