The remainder of this chapter documents the available mail server commands. Please note that these commands are those accepted by the PMDF mail server. Other implementations of mail servers exist, notably the BITNET list servers. While there is a fair amount of commonality amongst the commands accepted by many of the different mail servers, differences also exist. Do not expect these commands to work with other mail servers and do not expect other mail server commands to work with PMDF mail servers. When you are unsure of what sort of mail server you are dealing with, the first order of business should be obtaining help information for that server. Often this can be done by sending the command HELP to the server.