How to compose anonymous mail?

Would anybody tell me how to setup anonymous mail?

I am trying to setup an anonymous user who has a return email
address looks something like: trwe(_at_)bogus(_dot_)com

sendmail alias would do some of the tricks but the anonymous 
user will need to have a shell account to send out mail.

One of the procmail receipt I'd used:
   * !^FROM_DAEMON
   | formail -trI"From: trew(_at_)bogus(_dot_)com" \
   | $SENDMAIL -oi -t
Donot seem to work very well. I am still getting the real owner
of the mail from the header part. 

Any idea will be greatly appreciated.

Thanks,

-- 
Phong Ta
Motorola Advanced Messaging Group