[Exim] host lookup defer

Hi guys.

I'm using exim in a isolated network to control internal email. I have a fax server on the net to manage the fax stuff. My problem is that when people send emails to
Person%PhoneNumber@??? I always get this message at eximon:

10:32:42 11GkI6-0000P3-00 == wewe%555@??? R=lookuphost defer (-1): host lookup did not complete

I don´t know what kind of problem is. It´s seems to be a DNS problem, but i have the DNS localy , and the nslookup tool does the lookup fine.

I hope you can help me.

Thanks