Reviewing the source of a message provides valuable information such as the X-mailer, the return path, received address and time, message ID, to and from and subject information, date, priority, MIME version, and content type.
NOTE: Source review option needs to be enabled on Administration level. When enabled, user will see that expand source icon in Details tab is enabled. Otherwise expand source icon will be disabled.
Tip: If you cannot see the source information, click the expand icon. (Provided that it's been enabled on administration level)
How do I create a new e-mail message?