Before going into the DNS setup steps, let's take a moment and explain why this is necessary. If you're familiar with the basic concepts behind DNS, feel free to skip ahead to the relevant walkthrough for your organization.
At its simplest, a DNS entry is nothing more than a bit of text stored on your Web server that tells other computers on the Internet the Domain Name (the "D" and the "N" in "DNS") that should point to a specific IP address.
Without DNS entries being and shared by various ISPs and telecom providers, you wouldn't be able to type "www.google.com" into a Web browser and have it point to anything. Instead you'd have to type in the IP address for Google's home page directly: 188.8.131.52
Now imagine trying to memorize IP address strings for dozens, or hundreds of Web sites. Not very appealing, right? Hence why our benevolent Internet overlords—ISPs, telecom providers, and the non-profit Internet Corporation for Assigned Names and Numbers (ICANN)—promulgated the current DNS system.
Think of it like the address for a company's office location. The IP address would be the equivalent of, "1234 Main Street, Tallahassee, Florida, 32301." The DNS entry would be "ACME Incorporated." In conversation you could refer to ACME as "The company located at 1234 Main Street, Tallahassee Florida," which is technically accurate, but it's easier to just call it by its name, "ACME Inc."
For a more thorough review of basic DNS concepts, visit http://computer.howstuffworks.com/dns.htm
What we're going to do with Vision is similar to what happens when you set up a P.O. box at the Post Office. You don't "own" the physical box, the post office does, but everyone knows that mail being sent to and from the P.O. box belongs to you. You're the "authorized user" of the box.
We're going to set up an IP address on an InsideSales.com server that will be used as an intermediary "reference point" for sending and receiving email. After you update the appropriate DNS entries, other Web and email servers will view, or resolve the "owner" of the address back to you. It's basically like telling the post office, "Hey, this previously unassigned P.O. box is now registered to THIS person."
To add the DNS entries, we need to access a specific text file stored on your Web host. The entries will resolve two components, one letting Web servers know that the supplied IP address belongs to your Web domain, and another letting email servers know that mail service running through that IP address also belongs to your domain.
The purpose for all of this is to ensure successful mail delivery. You could theoretically use Vision without updating the DNS entries, but many mail servers would view emails as not originating from your domain. This would affect delivery, causing emails to regularly be flagged as spam.
Also, using DNS in this manner means that you are in control of your own mail reputation. You're not sharing a mail space or service with anyone else, meaning that if someone chooses to abuse their mail privileges, your mail reputation isn't penalized for their misdeeds.