[Exim] Exim 4.14 + Exchange 6 not talking

Has anyone had problems with exim 4.14 comunicating with MS exchange
server V6.

Exchange can recieve mail form my exim server, no problem but when exim
has to recieve mail form the exchange server, the sender gets the
following error "SMTP Error Code 442"
What can i do to resolve this ?

Many Thanks
Gregory Machin