Verifying software is always a great place to begin. I was also able to find a knowledge base article that might offer a few more troubleshooting steps that should guide you toward resolving your issue:
If you are not familiar with working through DNS changes the following information is linked to in the above article:
For information about how to change DNS settings in Mac OS X, see Editing DNS and search domain settings.
Thanks for reaching out to Apple Support Communities to find answers to your question.