Int 21 Fn 5F51  u - Lan Manager Enhanced Dos - Dospeekmailslot             [N]

   AX = 5F51h
   BX = handle
   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=5F35h,AX=5F4Fh,AX=5F50h,AX=5F52h