How to Add a Custom Domain to Your SUPPRESS Account
Overview
Custom Domains are domains (which you've purchased) that can be used to override the default Opt-Out Domain name provided with your SUPPRESS account. You can change domains at an account level, or override the domain being used by a specific Mailer, a group of Mailers or Opt-Out List.
A common use case for Custom Domains is assigning a Mailer or group of Mailers to their own Opt-Out Domain; this allows you to isolate the mailing activities of each partner, as to not affect others.
Add a Custom Opt-Out Domain, assign a Custom Opt-Out Domain to your account or Opt-Out Lists & Mailers.
Steps
1. Choose View Domains from the Settings drop-down menu.
2. Then select the Add a Domain button from the Domains page.
3. From the Add a Domain page select add your own Custom Domain link. 
If you would like to learn more about the benefits of using a Managed Domain, please review this article: What Is The OPTIZMO's Managed Domain & IP Service?
4. On the Domain Details page you will add the following...
Domain Title - is simply a useful title for you to describe your new Custom Domain. (ex. Internal Mailers Only).
Domain Name - is where you will add the new domain you purchased.
Notes - you can add any internal notes about this domain for your reference. This is not a required field.
*Please Note - for the Custom Domain to work, the CNAME DNS record must point to one of your managed OPTIZMO domains. This must be set before you can use this setting. A check will be performed on Saving.
5. Once you are finished adding the domain details and setting up the CNAME DNS record, select the Add Custom Domain button.
6. Now you should see the Custom Domain that you added on the Domains page.
If you have further questions, please contact us: support@optizmo.com