Int 16 Fn 4503  - Shamrock Software EMail - Specify Command-word For User  [e]

   AX = 4503h
   DL = port number (01h = COM1)
   DH = maximum execution time in clock ticks (00h = 5 seconds)
   ES:BX -> ASCIZ string with new user command-word

Return: AX = 4D00h if EMAIL installed on specified port

Notes: a single user command (consisting of only uppercase letters and digits)
     may be defined, and remains valid until it is overwritten or the
     EMAIL program terminates; the user command must be activated by
     calling AX=4504h at least once.
   an existing command word may be redefined with this function

See Also: AX=4504h,AX=4505h