Mailman module to allow posts of DKIM-signed messages which sent from specific domains

DKIMModerate.py

# Copyright (C) 2019 by TSUCHIYA Masatoshi <[email protected]>
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License
# as published by the Free Software Foundation; either version 2
# of the License, or (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
# USA.
#

"""This module implements DKIM based moderation.

USAGE:

(1) Put this file into the directory of Mailman handler modules, e.g.
/usr/lib/mailman/Mailman/Handlers/

(2) Add following codes to mm_cfg.py:

DKIMDOMAINPATTERN = "[@.]example\.jp$"
GLOBAL_PIPELINE[GLOBAL_PIPELINE.index('Moderate')] = 'DKIMModerate'

"""

import dkim
import email.utils
import re
from Mailman import mm_cfg
from Mailman.Handlers.Moderate import process as moderate_process
from Mailman.Logging.Syslog import syslog

def process(mlist, msg, msgdata):
    def dkimverify(message):
        if not message.get('DKIM-Signature'):
            gd = message.get('X-Google-DKIM-Signature')
            if gd:
                message.add_header('DKIM-Signature', gd)
        if dkim.verify(message.as_string()):
            syslog('error', 'DKIM signature of this message is verified')
            sender = (email.utils.parseaddr(message.get('From')))[1]
            if sender and re.search(mm_cfg.DKIMDOMAINPATTERN, sender):
                return True
        else:
            syslog('error', 'DKIM signature of this message is NOT verified')
        return False

    if mlist.generic_nonmember_action == 1 and dkimverify(msg):
        return
    return moderate_process(mlist, msg, msgdata)