The following is a screenshot of WYSIWYG content editor with Other Tags drop-down highlighted:

The following tags are available in the Other Tags drop-down:
- {{other.time_stamp}} – The tag is replaced by the current date and year.
- {{email.message_id}} – The tag is replaced by the email message ID. The email message ID is a combination of a Universal Unique Identifier (UUID) and a Sending Domain (DKIM) authenticator that the Marketing Cloud assigns to every campaign in the system.