Over the next few days, the Free Software Foundation will be making changes to our GNU Mailman systems, including lists.gnu.org, lists.nongnu.org, lists.libreplanet.org, lists.fsf.org, and lists.endsoftwarepatents.org, in order to address mailing list deliverability issues reported by many users.
I wanted to specifically let freetype-devel know about this since it is a fairly active list that is affected. Messages sent from users with strict DMARC policy domains like yahoo.com are often being rejected when sent to list subscribers by Mailman. See the end of this email for a technical overview of DMARC and DKIM. There are two ways to fix the issue by changing Mailman list settings. The first option, and the preferable way for discussion lists, is what we call the "unmodified message fix." There are Mailman list settings which modify the messages by adding a subject prefix (e.g. [list-name]) or a footer. Modifying the message breaks DKIM message signatures and thus DMARC. Following this option, we would turn those settings off. Many lists are already this way and there is no change for them. Instead of using the subject prefix to identify a list, subscribers should use the "List-Id" header, To, and Cc. List footer information can also be be put in the welcome email to subscribers and the list information page by list administrators. Related to this, on June 7th, we upgraded the version Mailman that we run. This fixed a bug where we were breaking the DKIM signature of any reply message. The second option is for lists which want or need to continue to modify the message, for example with subject prefix or footer settings. We would enable a Mailman list setting called dmarc_moderation_action: "Munge From". With this setting, if a strict DMARC sender sends to the list, we alter the headers of that message like so: A message sent to the list: To: al...@gnu.org From: Anne Example Person <aper...@example.com> Subject: Hi, I have a suggestion to improve x The message Mailman sends to list subscribers: To: al...@gnu.org From: Anne Example Person via Alist <al...@gnu.org> Reply-To: Anne Example Person <aper...@example.com> Subject: [alist] Hi, I have a suggestion to improve X Without going into all of the details, here's a few points about why we concluded the unmodified message fix is better for discussion lists. Email clients don't all treat munged messages the same way as unmunged, and humans read these headers so it can confuse people, causing messages not to be sent to the expected recipients. GNU Mailman has an option to do "Munge From" always, but does not recommend using it[1]. While we're not bound by what others do, it's worth noting that other very large free software communities like Debian GNU/Linux have adopted the unmodified message fix[2]. The unmodified messages fix avoids breaking DKIM cryptographic signatures, which show the message was authorized by the signing domain. New discussion lists' default settings will be to send unmodified messages. Existing discussion lists that add subject prefixes or footers will have "Munge From" turned on, and then we will email the list administrators and moderators asking if they are ok with changing to unmodified messages. If they do not object within 1 month, we will change their list settings to send unmodified messages. Sometimes the list administrators and moderators emails goes out of date. If you have the administration password for a list, please log in and check that they are up to date at the top of the "General Options" section of the list administration interface. For announcement lists that do not have discussion, munging does not have nearly as bad an impact. Announce lists with subject prefixes or footers will get "Munge From" applied. I will email the list owners and moderators to let them know about this issue and they can change to using unmodified messages if they want. Announce lists created in the future will send unmodified messages by default. Debbugs lists prepend a bug # to the subject. These will get "Munge From" applied. An example of a debbugs list is bug-gnu-emacs[3]. Debbugs maintainers can consider if there are any other changes they want. For -commit lists, commit messages are created by a program running on a single server, not the authors in the from headers. This means they cannot have valid DKIM signatures and so they will get "Munge From" applied and always need it. An example of a -commit list is gnuastro-commits[4]. For any Mailman list administrator who wants to change or look over the relevant settings: The dmarc_moderation_action setting is under "Privacy Options" subsection "Sender Filters". The only options that should be selected are "Accept" or "Munge From", along with corresponding changes to the subject_prefix option under "General Options", and msg_footer under "Non-digest options". A short DMARC technical overview: DMARC policy is a DNS txt record at a _dmarc subdomain. For example: $ host -t txt _dmarc.yahoo.com _dmarc.yahoo.com descriptive text "v=DMARC1; p=reject; pct=100; rua=mailto:dmarc_y_...@yahoo.com;" The only important thing there for our purpose is p=reject. p=reject means that conforming mail servers that receive mail with a from header of *@yahoo.com will reject that email unless it was either 1. sent from Yahoo's email servers, or 2. its DKIM signature is verified. A DKIM signature[5] is a public key cryptographic signature of the email body and some headers included in the message header "DKIM-Signature". A verified DKIM signature means that email body and signed headers have not been modified. Comprehensive resources about DMARC tend to downplay or ignore its problems, but some that have helped me are Wikipedia[6], the Mailman wiki[1], dmarc.org wiki[7], and the DMARC rfc[8]. [1]: https://wiki.list.org/DEV/DMARC [2]: https://lists.debian.org/debian-devel-announce/2015/08/msg00003.html [3]: https://lists.gnu.org/archive/html/bug-gnu-emacs/2019-06/threads.html [4]: https://lists.gnu.org/archive/html/gnuastro-commits/2019-06/threads.html [5]: https://en.wikipedia.org/wiki/DomainKeys_Identified_Mail [6]: https://en.wikipedia.org/wiki/DMARC [7]: https://dmarc.org/wiki/FAQ#senders [8]: https://tools.ietf.org/html/rfc7489 -- Ian Kelling | Senior Systems Administrator, Free Software Foundation GPG Key: B125 F60B 7B28 7FF6 A2B7 DF8F 170A F0E2 9542 95DF https://fsf.org | https://gnu.org _______________________________________________ Freetype-devel mailing list Freetype-devel@nongnu.org https://lists.nongnu.org/mailman/listinfo/freetype-devel