When your brand is set up for email, three different types of lists are created: Subscription Lists, Transaction Lists, and Test Lists. Use these lists to send emails to certain contacts.
Subscription Lists are designed to communicate promotional messages and general emails to your contacts from the brand. Creating multiple subscription lists allows your contacts to choose which emails they would like to receive from you by subscribing to some lists but not to others. For example, a contact may want to receive your weekly newsletter emails but not emails about special events.
Transaction Lists are used for campaign triggered content and emails that would be based off of account updates. All contacts will be added automatically to your transactional list. A brand can only have 1 transactional list.
Test Lists are used to send a test email message to a small group of users without influencing reporting stats.