According to the Marketing Cloud Account Engagement Email Basics, there are three mandatory components for an email to be saved in Marketing Cloud Account Engagement: a text version, a sender, and an unsubscribe link. A text version is required for accessibility and deliverability reasons, as some email clients or recipients may not support HTML emails. A sender is required to identify the source of the email and comply with the CAN-SPAM Act. An unsubscribe link is required to allow recipients to opt out of future emails and comply with the GDPR and other privacy regulations. Variable tags, dynamic content, and social posts are optional components that can enhance the personalization and interactivity of the email, but they are not required for saving the email draft.