Hey Simon,
Email headers contains valuable information about the sender so other than the primary information you would sometime need to include custom values in your mail headers, to better describe the email. Some examples of the custom values for the headers are X-priority to define the higher priority of the email and List Unsubscribe etc.
This specific function of Global Headers will help custom values for the mail headers to carry with the emails you send from the system. Creating a global header for the mail header will have a global effect on all outgoing emails, which means, values that you add here will be the part of the headers of every outgoing email from Mumara.
THankyou
