It is becoming standard practice to use both your domain name and the IP address your mailings are sent from as part of the formula in deciding if you are sending spam or legitimate mail. This benefits you in a few different ways.
- If you move to a new host or mailing system, your domain reputation will stay with you
- If you share an IP with other clients, your reputation will no longer solely depend IP alone
Here are a couple of recent articles regarding that talk more about sending emails and the use of domain reputation.