Int 21 Fn 5F50  u - LAN Manager Enhanced DOS - Dosreadmailslot             [N]

   AX = 5F50h
   BX = handle
   DX:CX = timeout
   ES:DI -> buffer

Return: CF clear if successful
       AX = bytes read
       CX = next item's size
       DX = next item's priority
   CF set on error
       AX = error code

See Also: AX=5F4Dh,AX=5F4Fh,AX=5F51h,AX=5F52h