A Sub-Mailer is created when you work with a network/agency that also has its own SUPPRESS account.  In this scenario, the partner will create a Linked List in their account which allows them to connect to your system at a Suppression List level.  Here is an article that speaks a little further about What is a Linked List?

You can find a Sub-Mailer in your account by going to a Mailer's profile page and scrolling down to the section called Sub-Mailers.  To learn more about the Mailer's Profile page, please review this article (add link)

If you have further questions, please contact us: support@optizmo.com