When you track traffic on your law firm blog or website, you many be presented with the IP addresses of visitors who came to your blog or website. How do you know to whom a specific IP address belongs? This website enables you to trace back a specific IP address to the domain (e.g., yourcompany.com) with which it is associated. The test performed is known as a Reverse DNS lookup.
Incidentally, some companies use filters to block emails based on reverse DNS lookup tests. What this test involves is looking at the domain name used in the "header" of your law firm's email alert or newsletter (e.g., the domain of the reply email address, the bounce address, etc.), and then comparing that domain to the domain associated with the IP address of the mail server that sent the email. A mismatch doesn't mean your email won't get delivered, but certainly a match improves deliverability.
To maximize deliverability of your law firm email alerts and newsletters, consider setting up a custom domain for your email campaigns that will ensure a match between the domain of the IP address of the server sending your email and the domain names in your email headers.