Can I have more than one Custom Domain active at a time?
You can have more than one Custom Domain in your account, but you can only have one of those domains assigned at the account level at any one time. So if you have two Custom Domains, you can assign one at the account level and one at an Opt-Out List level. To create Custom Domains, hover over the Settings Tab and on the sub-menu that appears, click on Custom Domains.