[Exim] problem with routing

Hello,

i've been using exim for some years now, and i 've never seen this kind of
problem :

when i try to deliver a message, it stays on the queue with : no route to
host
when i do traceroute, the host is found, is there something i'm missing ?

Exim version 3.15
OS linux, kernel 2.4.1


thanks for your advices

Pascal