To designate an address or hostname connected via CSNET
Was widely used in late 1980s, but is no longer in use
No registrations are possible, as this domain is not in the root
Appended to right of CSNET hostnames
.csnet is a hostname suffix that was used for identifying nodes in the Computer Science Network (CSNET) not directly connected to the Internet but reachable through special gateway systems. It was never installed as a top-level domain in the Domain Name System, but parsed in the message routing logic of mail transport agents (MTA). It was introduced in 1985.