How Messages Work in Transactional Mailings

From the Message tab, you can activate market testing and specify the mailbox settings for the mailing, the subject of the email, and any URL parameters you want to attach to links in the message.

In addition, you can create either plain text or HTML messages from scratch, from existing content, or by uploading HTML from another site. Creating a message in transactional mailings follows the same procedure as creating a message in broadcast mailings. See Create a Message in Broadcast Mailings.