help with a procmailrc recipe

To fight against increasingly aggressive spam mails, besides 
spam-assassin and a couple dozen filters I use to trash sure-spams, there 
still remain some mixed mails where I have to manually fish out good from 
bad or bad from good mails.

For this "small" portion of mails, I wrote a recipe to send automated 
inquery mails to verify if a suspecious mail is from a human-being: if it 
gets a human reply to confirm, the saved mail gets further delivered; if 
the inquery mail gets bounced, the saved mail gets deleted.  So far 
everything works fine except this last recipe to process bounce/delete:

:0
* ^FROM_DAEMON|^FROM_MAILER
{
    :0 w:bb.lock
    * B ?? Subject: verify mail you sent: ([0-9\.]{15}[A-Z]{9})
    THEMATCH = $MATCH

      :0 a
      | rm -f /var/mail/QUARRENTEEN/$THEMATCH

    :0 E:
    Mailerrors
}

The problem is that the saved file name is not caught by regular 
expression match. My auto-inquery mail "Subject:" line is like:

  Subject: verify mail you sent: 20141127.120132MUUNJUEDC

(Note this line is placed in the mail body in a bounce). I suspect if my 
regex is "perl" like and not supported by procmail or else?

Thanks in advance,

Zhiliang