SMTP uses commands and response to transfer message between a client and a server.
Each commands or reply is terminated by a two character ( carriage return and lien feel) end of line token .
Commands are sent from the client to the server. The format of a command is shown below it consists of a keyword followed by zero or more arguments. SMTP define 14 commands. The first five are mandatory. Every implementation must support these fie commands. The next three are often used and highly recommended. The last six are seldom used.