[Exim] Message frozen

Is there any reason this should have been frozen. I don't have any rules
to freeze on this error.
Other emails to this domain have gone through not a prob. I can't have
emails frozen on routing errors to this domain.
Running exim 3.14 on RH 5.2
----- Original Message -----
Sent: Thursday, September 07, 2000 10:21 AM
Subject: Message frozen


> Message 13Wpsv-0004QQ-00 has been frozen. The sender is
<thatperson@???>.
>
> The following address(es) have yet to be delivered:
> user@??? : lookup of host "gateway.this.domain.com" failed
in to_domain router
>

logs show this for that domain
2000-09-07 10:19:03 13Wpra-0004Ps-00 => user@??? R=to_domain
T=remote_smtp H=gateway.this.domain.com [203.23.53.x]
2000-09-07 10:21:54 13Wpsv-0004QQ-00 == user@??? R=to_domain
defer (-1): lookup of host "gateway.this.domain.com" failed in to_domain
router
2000-09-07 10:39:59 13Wq9a-0004YD-00 => user@??? R=to_domain
T=remote_smtp H=gateway.this.domain.com[203.23.53.x]

Here is the router

to_domain:
driver = domainlist
transport = remote_smtp
route_list = this.domain.com gateway.this.domain.com byname


Any suggestions to stop this these sort of errors from being frozen would
be muchly appreciated.
cya
Andrew


--
Vital papers will demonstrate their vitality by
spontaneously moving from where you left them to where
you can't find them.