How to stop a user from changing the 'From:' header.

7 msg	Postfix 2.2.5 on latest Solaris 9 x86
5 msg	Postfix Relay, and Pop-before-smtp
12 msg	Newb Question
13 msg	Best defense against this?
1 msg	undelivered mail problem - SOLVED
4 msg	Legal local-part
3 msg	virtual_alias_domains with mysql: 'User unknown...
6 msg	Submission port (587): howto to use differente ...
5 msg	When does smtpd_reject_unlisted_recipient kick in?
4 msg	Postfix 'falling back' on sasldb? I don't want ...
3 msg	Nested access maps (I think ;))
3 msg	Suppression of encoding bad header function in ...
4 msg	RE: Catchall ??
3 msg	problem with .forward files + forwarding loops
5 msg	Postfix Strange Behaviours
7 msg	Content filter question, based upon auth'ed or not
28 msg	Mail stuck in active queue for loooong time

How to stop a user from changing the 'From:' he...
\ rodolfo (20 Sep 2007)
. \ mouss (20 Sep 2007)
. \ Victor Duchovni (20 Sep 2007)
. . \ Jay Chandler (20 Sep 2007)
. . . \ Victor Duchovni (20 Sep 2007)
. . . . \ Jay Chandler (20 Sep 2007)
. . . . . \ Victor Duchovni (20 Sep 2007)
. . . . . . \ Jay Chandler (21 Sep 2007)
. . . . . . . \ Victor Duchovni (21 Sep 2007)
. . \ rodolfo (20 Sep 2007)
. . . \ mouss (21 Sep 2007)

10 msg	[Semi-OT] blocked port 465, anywhere?
7 msg	chroot problems on Nexenta (OpenSolaris)

Subject:	How to stop a user from changing the 'From:' header.
Group:	Postfix-users
From:	rodolfo
Date:	20 Sep 2007

Hello,

I have a Postfix installation which uses Cyrus-SASL for SMTP Auth. A
customer wants that his users, using e-mail clients like "The Bat", stop
changing the "From:" header, forging the "from" address.

Let's say, the user john (authenticated with his real login
and password) changes the From: field to peter and sends the
email to victim, making the Victim user to think that he's
getting email from peter (when the real sender was
john).

Is there any way to stop this with Postfix?

Thanks in advanced.