INT 15 - MultiDOS Plus - READ MAILBOX
AH = 06h
AL = mailbox number (00h-3Fh)
CX = size of buffer in bytes
ES:DI -> buffer for message
Return: AH = status
00h successful
CX = number of bytes copied
DX = actual length of message
02h invalid mailbox number
Note:   if the caller's buffer is not large enough, the message is truncated
and the remainder is lost
SeeAlso: AH=05h"MultiDOS"

See also: 1504

1506 - MultiDOS Plus - READ MAILBOX