Are you using transparent dns or sendmail?
Can u do a dns query from the firewall itself?
How are you routing traffic between the 2 internet links?
I meant transpared or split?
You cannot use two ISPs at the same time unless you route specific destination traffic to a downstream router of your non-default-route ISP.
You cannot use the DNS proxy at the same time you're using Split DNS (named, the BIND server) so make sure you're not doing that.
If you need to troubleshoot the issue I suggest you call in to Support.
I am using Transparent,
Thanks for your answers