[imp] How to maildrop?

[Mugendai]

Let me describe just what I'm wanting.
I want the server to run a set of filters on mail as it comes in to the 
SMTP(postfix).  I want the filters to be user based. I don't want the 
users to be real users, wanna use virtual users(which is what is 
currently done with the mailsystem, using 
postfix+mysql+amavis+spamassassin+courier and using IMP for webmail.

I'm wanting users to be able to set filters in the webmail system to 
filter the mail as it comes in, so that it will occur without the user 
having to use webmail.(mainly want webmail as a system to configure the 
filters)

I'm stuck at figuring out how to use IMP to do this.  From what I 
understand I need to use something like maildrop to do the filtering. 
But I dont understand just how I need to do this.

my mail transport is virtual, and my virtual transport is maildrop
atm..  maildrop is set up as:

maildrop  unix  -       n       n       -       -       pipe
   flags=DRhu user=vmail argv=/usr/local/bin/maildrop -d ${recipient}

So what I am unsure about here, is how maildrop is configured.  The man 
page is confiusing on this, I'm not sure how to set it up properly for 
my non-real user setup.  But anyway it goes, it looks to me like the way 
I have it now, the mail isn't gunna end up in the right place.
/var/spool/mail/

I am also not understanding how to configure Ingo so that it can 
configure the filters for maildrop.  This is all on one computer, do I 
really have to use FTP to transfer the file across the filesystem? 
Can't it just directly write to the disc?  If so how?  Is that what null 
is for?  I'dunno I cant find docs explaining that part of the format.

got the maildrop compatible version of Ingo, FYI

Please help, thanks alot