RoundCube - Authenticated user in header?

==== Required information ====
- iRedMail version: 1.9.2
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MySQL
- Linux/BSD distribution name and version: CentOS 6.5
====

Hello,

today one of my users changed the "identity" on RoundCube to another user, to send messages as him. In the mail headers, there's no reference to the autheticated webmail user. There is a way, in RoundCube or Postfix, to force a header like "X-Authenticated-User"? Or a way to disallow send messages when "from" is not the authenticated email account?

Thank you!