regexp_find()
  Recipient email address to index scanner, operating with regexp.
  
  It is useful only as lmtpd() scanner, because it operates on email
  recipients.
  
  Usage: regexp_find(key, scanners)
  
  Where: key is an string, which defines which variable to compare.
           Currently only "recipient" can be used here.
         scanners is an dictionary of scanners, each returned key from
           database must have coresponding key in this dictionary
  
  Example: regexp_find(
             'recipient',
             {
               '@somedomain.com$': b2f(libclam()),
               '@anotherdomain.sk$': spamassassind(),
               '': s2f(libclam())+spamassassind()
             }
           )
  
  Limitations: It is not possible to include one regexp_find() into another.
  
  New in version 0.9.0.