[imp] Using $imp['user'] to define a Spam reporting address

[John Brook]

Hello all,

 I have hit a brick wall on this one, any help would be much appreciated!

Background:
 I am in the process of setting up an email server and I want to
provide webmail on it, so I chose IMP ;-) I have a spam filter on the
server (DSPAM). I would like for the "Report as Spam" link in the IMP
message window to send email to spam-$username at myserver.com

Problem:
 I think that this line:

$conf['spam']['email'] = 'spam-' . $imp['user'] . '@myserver.com';

should do the job just fine. But it doesn't  8-(  Mail gets sent to
spam- at myserver.com, which causes Exim to spew an error!

Can anyone tell me what I'm doing wrong? I guess it will be something
fairly obvious, but several Google searches have turned up nothing...

System info:
Debian(testing)
Apache 1.3.29.0.2-4
PHP4 4:4.3.4-4
IMP3 3.2.2-3.1

(just let me know if you need more info to diagnose the problem.)

   Many thanks!

               John