Int 21 Fn 5F4F  u - LAN Manager Enhanced DOS - Dosmailslotinfo             [N]

   AX = 5F4Fh
   BX = handle

Return: CF clear if successful
       AX = max message size
       BX = mailslot size
       CX = next message size
       DX = next message priority
       SI = number of messages waiting
   CF set on error
       AX = error code

See Also: AX=5F4Dh,AX=5F4Eh,AX=5F50h