INT 15 - MultiDOS Plus - CHECK MAILBOX
AH = 05h
AL = mailbox number (00h-3Fh)
Return: AH = status
00h successful
DX = length of first message in queue, 0000h if no message
02h invalid mailbox number
SeeAlso: AH=06h"MultiDOS"

See also: 1504

1505 - MultiDOS Plus - CHECK MAILBOX