What must transactional messages NOT contain?

Transactional messages must not contain false or misleading header information as this is crucial for maintaining trust and transparency with recipients. Transactional emails are typically sent in response to actions taken by the user, such as order confirmations, shipping notifications, or account-related messages. As these communications often contain important information regarding transactions, it's essential that the content is truthful and accurately reflects the nature of the message.

Including false or misleading header information can lead to significant issues, including violations of email marketing laws such as the CAN-SPAM Act. This type of infringement can result in penalties and damage to the sender's reputation. On the other hand, it is perfectly acceptable for transactional emails to contain personalized content, unsubscribe links (as long as they are not mandatory), and mandatory privacy notices, as these elements enhance customer experience and compliance with legal requirements.