There are some cases where you cannot view your website or download emails from your domain but other people outside your office can. This problem is called selective browsing where the DNS servers of your ISP is having problem resolving to your domain.
The first step of resolving this is to report it to your ISP. Inform
them that your internet connection are selectively showing websites. This should at least be logged in their reports so they can have this fixed.
The next step is to go to www.opendns.com and change your computer's DNS settings manually.
The complete list of instructions per Operating System can also be found in that website.
If you have questions regarding this, Please email email@example.com