[Mailman-Users] Mailman integration with GoogleGroups:allowGroups Subscribers post directly

Mark Sapiro mark at msapiro.net
Sun Apr 17 17:47:43 CEST 2011

anatoly techtonik wrote:
>Let me concentrate on this part once more. I need only one group to be
>a frontend for one list. So I need only mails from this group to be
>delivered - not from all groups. If I understood correctly,
>+some_token is regenerated every post and it is "envelope address". My
>own @gmail.com address it not seen by Mailman when the message
>arrives, so the From: format is "My Name
><group_name+some_token at googlegroups.com>". Is this right?

No. You could answer these questions definitively for yourself by just
looking at the full headers of any message received from the Google

The message from the Google group will have headers

To: <the address of the google group>
From: <the name and address of the poster to the google group>

and will be sent with the envelope from (reflected in a Return-Path:
header) <group_name+some_token at googlegroups.com>

>I am not an administrator and can't validate this information. Just to
>make clear about the situation. The problem with just subscribing
>group address that when I post through the group (not being subscribed
>to the list), my post seems to appear in group only, but not on
>mailing list. I don't receive any notifications or bounces. But when I
>subscribe to the list, my post seem to pass through.

I think you are saying that if you subscribe the Mailman list to the
Google group and post to the Google group, your post is sent from the
Google group to the Mailman list and is accepted by the Mailman list.
If this is the case, and if the Mailman list accepts posts only from
list members, then this works because you are a member of the Mailman
list. It will also work for any other poster to the Google group who
is also a member of the Mailman list. The issue I am trying to help
solve is for posts to the Google group from people who are not members
of the Mailman list.

>>>Is it possible to add an option to Mailman itself to strip +token
>>>before processing email addresses?
>> Only by modifying code.
>Does it qualify as a feature request?

Anything can be requested.

Feature requests can be submitted to the bug tracker at

>>>Does email standard allow to use +token addresses for multiple users?
>> I do not understand the question. There will be one message from the
>> Google Group to the Mailman list. That message's envelope sender will
>> have a unique token so if it bounces, Google can easily tell which
>> recipient bounced. The messages from the Google Group to other Google
>> Group members will each have their own unique token.
>I see. I thought that if +token is something optional and that email
>standard specifies that "email+something at domain.com" is equivalent to
>"email at domain.com" and denotes the same recipient, and that email
>agents are not required to process the +part, then Mailman could just
>ignore it.

The Mail RFCs 2822 and 5322 specify regarding the local-part of an
address (the part left of the @)

   The local-part portion is a domain dependent string.  In addresses,
   it is simply interpreted on the particular host as a name of a
   particular mailbox.

I.e., it is up to the receiving domain to assign meaning to any xxx+yyy
local part. It is fairly common for the '+yyy' part to be ignored and
the 'xxx' part to be treated as the recipient, but as far as I know,
there is no standard governing this. Some MTAs use a '-' instead of or
in addition to a '+' as the delimiter, some may use other characters
and some do not recognize this kind of 'subaddressing' at all.

>>>> Thus you are left with a couple of other options. If the Google group
>>>> is set to include a Reply-To: <group_name at googlegroups.com> header in
>>>> delivered posts, and if <group_name at googlegroups.com> is a member of
>>>> the mailman list (with no password reminders and no mail delivery),
>>>> Mailman.Message.get_senders() will return that address in the senders
>>>> list and Mailman will consider the post from a member.
>The group is set into "Replies are sent to the whole group." mode. But
>the subscribed address is <group_name+token at googlegroups.com>. Now I
>see where the problem is.


>>>I'd like to ensure there is some kind protection to
>>>avoid spam that pretends to be from the Group. The same concern is
>>>about X-BeenThere header solution.
>> It doesn't take much sophistication to craft and send an email message
>> with anything one wants in the headers. People who want to can already
>> easily spoof the address of any list member in the From: header of a
>> message to fool Mailman into accepting the post as from a list member.
>I thought there is a reverse MX check to validate the message was sent
>from the IP that belongs to MX record for this domain.

Your own incoming MTA can implement any such tests it wants, and there
is a standard (SPF) addressing this, but such tests tend to reject
lots of legitimate mail, e.g. mail redirected via a .forward. In any
case, such tests when used will test the domain of the envelope
sender, not the domain of the From: header.

>>>> So, if you add <group_name at googlegroups.com> as a member of the mailman
>>>> list (with no password reminders and no mail delivery), and either set
>>>> the google group "Replies to messages" =C2=A0to "Replies are sent to the
>>>> whole group" or add the above SENDER_HEADERS line to mm_cfg.py, posts
>>>> arriving via the group will be seen as member posts.
>>>If I set "no mail delivery" then how the Group receive messages for
>>>reading from the web?
>> No mail delivery is a per user option. You set no mail delivery and no
>> password reminders for only the Google Groups address which is a
>> member of the Mailman list so that Mailman doesn't send the post back
>> to the Google Group. Delivery to other members of the Mailman list is
>> unaffected by this.
>Still can't understand how Google Group receive messages if Mailman
>doesn't send anything to its address. Do you mean that "no mail
>delivery" means that Mailman still sends all messages to Groups
>address except messages that were posted from this group (containing
>Group address in Reply-To: header)?

user at example.com sends a post to group at googlegroups.com. Post is
delivered to group members including mailman_list at example.net. Message
from group contains Reply-To: <group at googlegroups.com> and
group at googlegroups.com is a member of mailman_list at example.net so
message will be accepted by the Mailman list. Do you now want the
Mailman list to send the message back to the Google group?

If you wish to follow up further, please say exactly what you want to
happen when

1) member of Google group who is not member of Mailman list posts to
Google group.
2) member of Google group who is member of Mailman list posts to Google
3) member of Mailman list who is not member of Google group posts to
Mailman list.
4) member of Mailman list who is member of Google group posts to
Mailman list.

Mark Sapiro <mark at msapiro.net>        The highway is for gamblers,
San Francisco Bay Area, California    better use your sense - B. Dylan

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