Procmail script for white and black lists

# $HOME/.procmailrc for $LOGNAME in a Linux host
# logging by 'formail -l' rather than by procmail
# logs of the last 3 days available for the user
LOGABSTRACT=off
LOGF=$HOME/mail.log
DOMAIN=your.domain   #modify appropriately

# s.lst   filtering status, containing ON or OFF
# c.lst   contains code (password) to appear in plussed alias between + and @
#         in automatic request, has to be other than 00 (see [1] and [7]),
# w.lst   white list of addresses
# b.lst   black list of addresses
# r.lst   contains request to send an amty message to the plussed alias

# [1] message to the address from which request is sent (see [7]), discard,
# thus blocking non-delivery messages and bouncing loops
:0
* $ ^To:.*$LOGNAME\+00
| formail -l discarded >> $LOGF
 
# [2] message from MAILER-DAEMON, accept irrespective of filtering
:0
* ^From:.*MAILER-DAEMON
{
   :0 ch
   | formail -l accepted >> $LOGF

   :0
   ${DEFAULT}
}

# [3] message to the coded address, put sender's address on white list,
# send acknowledgment,
:0
* ? formail -x"To:" | fgrep + | fgrep -c -f $HOME/c.lst
{
   :0 ch
   | formail -l whitelisted >> $LOGF

   # extract sender's address proper (w/o < >)
   :0 h
   EADDR=| formail -x"From:" | sed 's/^\([^@]*[ <]\)//' | sed 's/\([ >]\).*$//'

   # append sender's address to white list, if it's not there already
   :0 ch
   * ! ? fgrep -s $EADDR $HOME/w.lst
   | echo $EADDR >> $HOME/w.lst

   :0
   | (formail -r;\
     echo Thank you. From now on, your messages to $LOGNAME@$DOMAIN;\
     echo will be accepted with no further obstacles.;\
     echo Please, resend your original message.)\
     | $SENDMAIL -t -oi
}

# [4] if filtering is OFF, accept everything
:0 
* ? fgrep -s OFF $HOME/s.lst
{
   :0 ch
   | formail -l accepted >> $LOGF

   :0
   ${DEFAULT}
}

# [5] message from an address on white list,
# tolerate plussed-numbered addresses, accept
:0
* ? test -s $HOME/w.lst
* ? formail -x"From:" -x"Reply-To"\
    | sed 's/\(\+[^@ <]*\)@/@/ig' | fgrep -is -f $HOME/w.lst
{
   :0 ch
   | formail -l accepted >> $LOGF

   :0
   ${DEFAULT}
}

# [6] message from an address on black list, discard
:0 h
* ? test -s $HOME/b.lst &&\
    formail -x"From:" -x"Reply-To" \
    | sed 's/\(\+[^@ <]*\)@/@/ig' | fgrep -is -f $HOME/b.lst
| formail -l discarded >> $LOGF

# [6a] message w/o From: or Reply-To:
     :0 h
     * ? test -z `formail -x"From:"`
     | sed s/MAILER-DAEMON/UNKNOWN/ | formail -l discarded >> $LOGF

# [7] message from an address on neither list, discard and
# send the request to the sender from $LOGNAME+00 address, see [1]
:0
{
  :0 ch
  | formail -l challenged >> $LOGF

  :0 h
  | (formail -r -I"From: $LOGNAME+00@$DOMAIN";\
    cat $HOME/r.lst) | $SENDMAIL -t -oi -f$LOGNAME+00@$DOMAIN
}
# 20 Jun 2008: modify [6] to simplify tests of w.lst and b.ls
#              add [6a]    for empty From: and Reply-To:
# 29 Jan 2005: correct [6] for empty black list
# 19 Jan 2005: correct [5] and [6] for user@ and @domain.name
# 29 Dec 2004: strict full address, no prefixes in [5] and [6]
# 29 Mar 2004: correct [3] for code eq username, and [5] for empty white list
#  3 Mar 2004: accepting plussed (+00) addresses to break possible deadlock
#              between 2 people using pef [5]
#  2 Oct 2003: logging by formail -l discarded|challenged|whitelisted|accepted
# 29 Jul 2003: correct extraction of sender's address in [3]
# 22 Jul 2003: add flags fh in [7]