Thanks you for sharing your idea. It will be considered for future versions of MDaemon. Currently, you can require users to send email using their email address by enabling the SMTP Authentication options for “Authentication is always required when mail is from local accounts” and “Authentication credentials must match those of the email sender”, however, with these options enabled there is not a way to allow one user to send on behalf of another user.
Thank you for submitting your idea, it will be considered for future versions.Romme, Ben commented
In Addition the separate WorldClient Server machine furthermore should implements the ActiveSync functionality. Then we can place this machine in a DMZ to serve external clients (WebAccess or SmartPhones). This would be a huge security improvement.