This article will show the steps on how you can view the complete email header in Roundcube Webmail
1) Login to Webmail using the URL (http://domainanme/webmail)
2) Select on Read Mail Using RoundCube
3) Double click on the email that you wish to view the header for
4) Click on the option "More" → "Show Source"
5) You are then able to view the complete email header of the email