This plugin will parse .eml or .msg files for email message headers, including x-headers, and will also color IPv4 and IPv6 addresses for ease of readability. Note: requires Sublime Text build 3092 or higher.
Open Sublime Text 3 and navigate to Preferences > Browse Packages… This should open the location on the file system under which Sublime Text 3 stores its packages.
Drop the “EmailHeader.sublime-syntax” within the "User" directory and the software should automatically add an “Email Header” syntax option in the lower right-hand corner. Any files with the .eml and .msg extensions will have this syntax definition automatically applied.