[rt-users] Problems with sendmail From: header

[Matias K.]

Hello! 
Im using rt3 on Debian Sarge with sendmail. I'm having a bit troubles
with sendmail. RT gets incoming emails with fetchmail just fine, but
when it autoreplys to ticket-senders the email seems to be coming from
www-data at localhost.localdomain.
This has something to do with sendmails trusted-users? 
I was browsing the list earlier and found out somebody had the similar
kind of problems and it was replied that go check the articles on
www.fsck.com/rtfm, there you'll find the solution. I could find it
there :)
Is someone able to help me or point me to an page with a solution?
Thank you in advance.