Dear exclist; About the instant messaging in exchange server2000, i have 2 server with 2 diferent network, first server is A class and the second is B class and the communication is ok. and there is instant messaging in A class. But when all user in A class use msn exchange messenger service to send message the other user to the same network in A class, there is no problem. but if user in A class send message to user in B class (over the other domain), there's a problem (the message cannot deliver), but if user in B class send message to A class, it's ok. and so i check it up to website log, and all ip client in B class notes ip_server(in B class), not detect own ip client (ip client in B class). Please help me, what should i do to fix it up? I need your all suggest... Regards; Amos