I manage an SBS 2011 Server that started acting up a few days ago.
Internet is not accessible most times. After a FlushDNS, a few sites work for a little while.
Emails work to some domains. No particular pattern.
RDP, RWA and OWA can be accessed.
Ran Connect to Internet, Set up your Internet Address and Fix my Network wizards a few times.
DNS has two forwarders. Tried to update root hints but none of the servers resolve.
Tried using different DNS servers as forwarders.
Swapped modem/router, switch, replaced network cables.
Getting desperate now.