Implement new drop_cc switch.

7 files changed, 34 insertions, 3 deletions

diff --git a/Mailman/Defaults.py.in b/Mailman/Defaults.py.in
index 594674ca..b45abf7b 100755
--- a/Mailman/Defaults.py.in
+++ b/Mailman/Defaults.py.in
@@ -1443,6 +1443,13 @@ OWNERS_CAN_PRESERVE_FILTERED_MESSAGES = Yes
 # Check for administrivia in messages sent to the main list?
 DEFAULT_ADMINISTRIVIA = Yes
 
+# The process which avoids sending a list copy of a message to a member who
+# is also directly addressed in To: or Cc: can drop the address from Cc: to
+# avoid growing a long Cc: list in long threads.  This can be undesirable as
+# it can break DKIM signatures and possibly cause confusion.  To avoid changes
+# to Cc: headers, set the list's drop_cc to No.
+DEFAULT_DROP_CC = Yes
+
 
 
 #####
diff --git a/Mailman/Gui/General.py b/Mailman/Gui/General.py
index dfde6309..86ddf933 100644
--- a/Mailman/Gui/General.py
+++ b/Mailman/Gui/General.py
@@ -505,6 +505,19 @@ class General(GUIBase):
                  here."""))
                 )
 
+        # Do we munge Cc: in AvoidDuplicates.py
+        rtn.append(
+            ('drop_cc', mm_cfg.Radio,
+             (_('No'), _('Yes')), 0,
+             _('Should duplicate avoidance drop addresses from Cc: headers'),
+             _("""The process which avoids sending a list copy of a message to
+               a member who is also directly addressed in To: or Cc: can drop
+               the address from Cc: to avoid growing a long Cc: list in long
+               threads.  This can be undesirable as it can break DKIM
+               signatures and possibly cause confusion.  To avoid changes to
+               Cc: headers, set this to No."""))
+             )
+
         # Discard held messages after this number of days
         rtn.append(
             ('max_days_to_hold', mm_cfg.Number, 7, 0,
diff --git a/Mailman/Handlers/AvoidDuplicates.py b/Mailman/Handlers/AvoidDuplicates.py
index 25c1b410..0e6e2229 100644
--- a/Mailman/Handlers/AvoidDuplicates.py
+++ b/Mailman/Handlers/AvoidDuplicates.py
@@ -53,6 +53,7 @@ def process(mlist, msg, msgdata):
         explicit_recips[addr.lower()] = True
     # Figure out the set of explicit recipients
     ccaddrs = {}
+    munge_cc = False
     for header in ('to', 'cc', 'resent-to', 'resent-cc'):
         addrs = getaddresses(msg.get_all(header, []))
         if header == 'cc':
@@ -88,6 +89,7 @@ def process(mlist, msg, msgdata):
                 newrecips.append(r)
             elif ccaddrs.has_key(r.lower()):
                 del ccaddrs[r.lower()]
+                munge_cc = True
         else:
             # Otherwise, this is the first time they've been in the recips
             # list.  Add them to the newrecips list and flag them as having
@@ -96,10 +98,13 @@ def process(mlist, msg, msgdata):
     # Set the new list of recipients
     msgdata['recips'] = newrecips
     # RFC 2822 specifies zero or one CC header
-    if ccaddrs:
+    if ccaddrs and mlist.drop_cc and munge_cc:
+        # There are remaining Ccs and we've dropped one or more and the list
+        # allows changing.
         change_header('Cc',
         COMMASPACE.join([formataddr(i) for i in ccaddrs.values()]),
         mlist, msg, msgdata)
-    else:
+    elif not ccaddrs and mlist.drop_cc:
+        # The list allows changing and there are no remaining Ccs
         del msg['cc']
 
diff --git a/Mailman/MailList.py b/Mailman/MailList.py
index f4b38b49..b85b1427 100644
--- a/Mailman/MailList.py
+++ b/Mailman/MailList.py
@@ -386,6 +386,7 @@ class MailList(HTMLFormatter, Deliverer, ListAdmin,
         self.obscure_addresses = mm_cfg.DEFAULT_OBSCURE_ADDRESSES
         self.admin_member_chunksize = mm_cfg.DEFAULT_ADMIN_MEMBER_CHUNKSIZE
         self.administrivia = mm_cfg.DEFAULT_ADMINISTRIVIA
+        self.drop_cc = mm_cfg.DEFAULT_DROP_CC
         self.preferred_language = mm_cfg.DEFAULT_SERVER_LANGUAGE
         self.available_languages = []
         self.include_rfc2369_headers = 1
diff --git a/Mailman/Version.py b/Mailman/Version.py
index f607c126..dd43f7d0 100644
--- a/Mailman/Version.py
+++ b/Mailman/Version.py
@@ -37,7 +37,7 @@ HEX_VERSION = ((MAJOR_REV << 24) | (MINOR_REV << 16) | (MICRO_REV << 8) |
                (REL_LEVEL << 4)  | (REL_SERIAL << 0))
 
 # config.pck schema version number
-DATA_FILE_VERSION = 111
+DATA_FILE_VERSION = 112
 
 # qfile/*.db schema version number
 QFILE_SCHEMA_VERSION = 3
diff --git a/Mailman/versions.py b/Mailman/versions.py
index d317a46d..6f83df16 100644
--- a/Mailman/versions.py
+++ b/Mailman/versions.py
@@ -508,6 +508,7 @@ def NewVars(l):
                        mm_cfg.DEFAULT_EQUIVALENT_DOMAINS)
     add_only_if_missing('new_member_options',
                         mm_cfg.DEFAULT_NEW_MEMBER_OPTIONS)
+    add_only_if_missing('drop_cc', mm_cfg.DEFAULT_DROP_CC)
     # Emergency moderation flag
     add_only_if_missing('emergency', 0)
     add_only_if_missing('hold_and_cmd_autoresponses', {})
diff --git a/NEWS b/NEWS
index 01f8a34a..bdb7fd7e 100644
--- a/NEWS
+++ b/NEWS
@@ -34,6 +34,10 @@ Here is a history of user visible changes to Mailman.
       now has a feature to sync the list's membership with a list of email
       addresses as with the bin/sync_members command.
 
+    - There is a new drop_cc list attribute set from DEFAULT_DROP_CC.  This
+      controls the dropping of addresses from the Cc: header in delivered
+      messages by the duplicate avoidance process.  (LP: #1845751)
+
   i18n
 
     - The Japanese translation has been updated by Yasuhito FUTATSUKI.