[exim] get rid of "ipv6 network unreachable"

Hi,

next question : any way to get rid of those messages, without activating
ipv6 ? :)

2011-10-28 17:11:43 1RJo5v-0002UB-Fx tahini.csx.cam.ac.uk
[2001:630:212:8:204:23ff:fed6:b664] Network is unreachable
2011-10-28 17:11:45 1RJo5v-0002UB-Fx => exim-users@??? R=dnslookup
T=remote_smtp H=tahini.csx.cam.ac.uk [131.111.8.192]

best regards,

M.Schwarz