The Domain Name System (DNS) is a directory service. It is the method computers use to translate names into IP addresses. When a computer cannot access DNS, your web browser will not be able to find web sites, and you will not be able to send or receive email.
DNS resolution of any address type can be confirmed using Argent Active Directory Rules.
Verify your Load Balancer is being used by resolving the A record for www.YourSiteHere.com.
Ensure external email can properly access your Mail Gateway by resolving its MX record.