help with processing "user+detail(_at_)foo" address

Hi,

I've been trying to use the "user+detail(_at_)foo" addressing option  
with procmail.  I saw a post a while back describing how to use this  
option, but I can't seem to get it to work.

I try to sendmail to "kykim+test" and I want the message to go a  
file named "test" or something like that.  The message ends up going  
to my mail spool file.

my .procmailrc looks like this:
        VERBOSE=on
        MAILDIR=$HOME/mail
        PMDIR=$HOME/.procmail
        LOGFILE=$PMDIR/log

        DETAIL=$1
        :0:
        * $DETAIL ?? ^^[^/ ]+^^
        IN.$1.spool

the log file reports the following:
        procmail: Assigning "DETAIL="
        procmail: No match on "^^[^/ ]+^^"
        procmail: Locking "/usr/spool/mail/kykim.lock"
        procmail: Assigning "LASTFOLDER=/usr/spool/mail/kykim"
        procmail: Opening "/usr/spool/mail/kykim"
        procmail: Acquiring kernel-lock
        procmail: [429] Wed Dec 13 12:29:51 1995
        procmail: Unlocking "/usr/spool/mail/kykim.lock"
        From kykim(_at_)truth(_dot_)harvard(_dot_)net  Wed Dec 13 12:29:50 1995
         Subject: testing user+detail
          Folder: /usr/spool/mail/kykim                         427
        procmail: Notified comsat:"kykim(_at_)20182:/usr/spool/mail/kykim"

As you can see, the variable DETAIL is not getting set.  Anyone  
have any ideas why?

Thanks,
-kevin