remail: Retrieve sender information

For open lists and especially contact points the 'From' mangling is
suboptimal as the senders email address is not contained in the mail
itself. Due to re-encryption a eventual signature is not longer intact
which means that the GPG key or the S/MIME certificate which are embedded
into the signature are not transported either.

Add infrastructure to collect sender information including key/certificate
if available and attach it to the mail. The first attachment contains
sender information and the second one if available contains the key or the
certificate.

The information is only stored when the config switch is enabled and the
sender is not subscribed to the list.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

Documentation/man5/remail.config.rst

@@ -260,9 +260,10 @@ The list base configuration for each list consists of the following items:
   .. code-block:: yaml
 
      listname:
-      enabled:           True
-      moderated:         True
-      listid:            ...
+      enabled:            True
+      moderated:          True
+      attach_sender_info: False
+      listid:             ...
       archive:
         ...
       listaccount:
@@ -276,8 +277,9 @@ The list base items:
   .. code-block:: yaml
 
      listname:
-      enabled:           True
-      moderated:         True
+      enabled:            True
+      moderated:          True
+      attach_sender_info: False
 
   enabled:
 
@@ -292,6 +294,16 @@ The list base items:
     with a subscriber. Mails from non-subscribers are not delivered to the
     list, they are delivered to the list administrator
 
+  attach_sender_info:
+
+    Collects information about the sender, email-address, encryption method
+    and if the mail is signed the GPG key or S/MIME certificate contained
+    in the signature. This information is attached to the original mail as
+    two seperate attachments (text info and key/certificate) if this is
+    enabled and the sender is not subscribed to the list. This is for open
+    lists and especially contact points so that the subscribers are able
+    to contact the sender.
+
   listid:
 
     Optional item to override the default list-id with a custom value.

remail/config.py

@@ -261,6 +261,7 @@ class archive_options(object):
 list_defaults = {
     'enabled'             : False,
     'moderated'           : False,
+    'attach_sender_info'  : False,
 }
 
 class list_config(object):

remail/gpg.py

@@ -175,7 +175,7 @@ class gpg_crypt(object):
         msg_set_payload(msg, pl)
         return msg
 
-    def decrypt(self, msg):
+    def decrypt(self, msg, sinfo):
         '''
         Try to handle received mail with PGP. Return decoded or plain mail
         '''

remail/mail.py

@@ -20,6 +20,41 @@ import time
 import sys
 import re
 
+class sender_info(object):
+    def __init__(self, msg):
+        self.mfrom = msg.get('From')
+        self.info = None
+
+    def get_info(self):
+        info = 'Sent from: %s\n' %self.mfrom
+        if self.info:
+            info += self.info.get_info()
+        else:
+            info += 'No GPG/SMIME info available'
+        return info
+
+    def store_in_msg(self, msg):
+        # Convert the message into a multipart/mixed message
+        ct = msg.get_content_type()
+        if ct != 'multipart/mixed':
+            msg.make_mixed()
+
+        # Attach the sender information as plain/text
+        msg.add_attachment(self.get_info())
+
+        if not self.info:
+            return
+
+        # Check whether the GPG key or the S/MIME cert is
+        # available and attach it.
+        fname, data, maintype, subtype = self.info.get_file()
+        if fname:
+            if maintype != 'plain':
+                msg.add_attachment(data, filename=fname, maintype=maintype,
+                                   subtype=subtype)
+            else:
+                msg.add_attachment(data, filename=fname)
+
 def sanitize_headers(msg):
     '''
     Sanitize headers by keeping only the ones which are interesting

remail/maillist.py

@@ -7,7 +7,7 @@
 from remail.mail import msg_set_header, msg_force_msg_id, send_mail
 from remail.mail import msg_sanitize_incoming, msg_is_autoreply
 from remail.mail import get_raw_email_addr, decode_addrs
-from remail.mail import msg_from_string
+from remail.mail import msg_from_string, sender_info
 
 from remail.smime import smime_crypt, RemailSmimeException
 from remail.gpg import gpg_crypt, RemailGPGException
@@ -138,7 +138,7 @@ class maillist(object):
         mbox.add(msg)
         mbox.close()
 
-    def decrypt_mail(self, msg):
+    def decrypt_mail(self, msg, sinfo):
         '''
         Decrypt mail after sanitizing it from HTML and outlook magic
         and decoding base64 transport.
@@ -147,9 +147,9 @@ class maillist(object):
 
         msg_plain = None
         if self.smime:
-           msg_plain = self.smime.decrypt(msg)
+           msg_plain = self.smime.decrypt(msg, sinfo)
         if not msg_plain:
-            msg_plain = self.gpg.decrypt(msg)
+            msg_plain = self.gpg.decrypt(msg, sinfo)
         return msg_plain
 
     def disable_subscribers(self, addrs, msgid):
@@ -180,7 +180,11 @@ class maillist(object):
         subj = prefix + msg['Subject']
         msg_set_header(msg, 'Subject', subj)
 
-    def moderate(self, msg, dest):
+    def is_subscribed(self, mfrom):
+        r = self.config.subscribers.has_account(mfrom)
+        return r or self.config.admins.has_account(mfrom)
+
+    def moderate(self, msg, dest, mfrom):
         '''
         If the list is moderated make sure that the sender of a mail
         is subscribed or an administrator. This checks also aliases.
@@ -188,10 +192,7 @@ class maillist(object):
         if not self.config.moderated:
             return False
 
-        mfrom = get_raw_email_addr(msg.get('From'))
-        r = self.config.subscribers.has_account(mfrom)
-        r = r or self.config.admins.has_account(mfrom)
-        if not r:
+        if not self.is_subscribed(mfrom):
             self.modsubject(msg, '[MODERATED] ')
             dest.toadmins = True
             dest.accounts = self.config.admins
@@ -219,7 +220,7 @@ class maillist(object):
             dest.toadmins = True
             dest.accounts = self.config.admins
 
-    def mangle_from(self, msg):
+    def mangle_from(self, msg, mfrom):
         '''
         Build 'From' string so the original 'From' is 'visible':
         From: $LISTNAME for $ORIGINAL_FROM <$LISTADDRESS>
@@ -227,23 +228,25 @@ class maillist(object):
         If $ORIGINAL_FROM does not contain a name, mangle the email
         address by replacing @ with _at_
         '''
-        mfrom = msg.get('From').split('<')[0].replace('@', '_at_').strip()
         return '%s for %s <%s>' % (self.config.name, mfrom,
                                    self.config.listaddrs.post)
 
     def do_process_mail(self, msg, dest):
+
+        msgid = msg.get('Message-Id', '<No ID>')
+        msgto = msg.get('To')
+        msgfrom = get_raw_email_addr(msg.get('From'))
+        sinfo = sender_info(msg)
+
         # Archive the incoming mail
         self.archive_mail(msg, incoming=True)
         # Destination was already established. Check for bounces first
         self.check_bounces(msg, dest)
         # Check for moderation
-        self.moderate(msg, dest)
-
-        msgid = msg.get('Message-Id', '<No ID>')
-        msgto = msg.get('To')
+        self.moderate(msg, dest, msgfrom)
 
         try:
-            msg_plain = self.decrypt_mail(msg)
+            msg_plain = self.decrypt_mail(msg, sinfo)
         except Exception as ex:
             txt = 'Failed to decrypt incoming %s to %s\n' %(msgid, msgto)
             self.logger.log_exception(txt, ex)
@@ -251,7 +254,12 @@ class maillist(object):
 
         self.archive_mail(msg_plain, admin=dest.toadmin)
 
-        mfrom = self.mangle_from(msg)
+        mfrom = self.mangle_from(msg, msgfrom)
+        # Save sender information in the outgoing message?
+        if self.config.attach_sender_info:
+            # Only do so for non-subscribers
+            if not self.is_subscribed(msgfrom):
+                sinfo.store_in_msg(msg_plain)
 
         for account in dest.accounts.values():
             if not account.enabled:

remail/smime.py

@@ -158,7 +158,7 @@ class smime_crypt(object):
 
         return None
 
-    def decrypt(self, msg):
+    def decrypt(self, msg, sinfo):
         try:
             envto = msg.get('To', None)
             msgid = msg.get('Message-Id', None)