SMTP command

SMTP command
ref: http://www.freesoft.org/CIE/RFC/821/index.htm

HELLO (HELO)
MAIL (MAIL)
RECIPIENT (RCPT)
DATA (DATA)
SEND (SEND)
SEND OR MAIL (SOML)
SEND AND MAIL (SAML)
RESET (RSET)
VERIFY (VRFY)
EXPAND (EXPN)
HELP (HELP)
NOOP (NOOP)
QUIT (QUIT)
TURN (TURN)