Int 21 Fn 5F40  u - LAN Manager Enhanced DOS - Local Netmessagebuffersend  [N]

   AX = 5F40h
   DS:DX -> NetMessageBufferSend parameter structure (see below)

Return: AX = error code

Format of NetMessageBufferSend parameter structure:
Offset Size    Description
 00h   DWORD   -> recipient name (name for specific user, name* for domain
           name wide, * for broadcast)
 04h   DWORD   -> buffer
 08h   WORD    length of buffer