A small company runs SBS 2003 as a router connecting to the Internet. The SBS DC also Exchange server. They told me that some email might be dropped and they had Event ID: 2012, Event Source: smtpsvc and Description: SMTP could not connect to the DNS server '126.96.36.199'. The protocol used was 'UDP'. It may be down or inaccessible.
I asked them to run nslookup. Here is the result.
DNS request timed out.
timeout was 2 seconds.
*** Can't find server name for address 188.8.131.52: Timed out
Default Server: UnKnown
Also both NICs DNS point to the ISP DNS 184.108.40.206. After they changed the internal DNS to 192.168.1.2 nslookup looks good and they don’t have Event ID 2012 any more. However, the workstations have a problem access the Internet. For example, if you browse yahoo.com from a workstation, you may receive the page cannot be displayed. But, after you access the yahoo.com from server (the server never has a problem to access the Internet), then the workstation can access the yahoo.com. If you try msn.com on the workstation, the same thing happens until you open msn.com on the server.
The all server and workstations were rebooted. Actually, whenever they reboot a workstation, the workstation may not be able to access the yahoo.com until the server tries first.