retry time not reached for any host after a long failure period

Hi,

I have a machine running exim4 in my network. It has a public IP, and a private IP. It generates email from a VOIP system, and relays it to an exchange server in the network.

However, no emails go out.. They all have the error message:

retry time not reached for any host after a long failure period

. I can ping the mail server. I can send mail via telnet. Can someone point me in the right direction?

Thanks
David