Just a note that may help some people.
After a bit of a learning curve, managed to get Mailman3 working in Debian 10 using the Debian package.
I have mailman3-full + exim4 + apache2 setup:
I did quite a lot of testing and getting it working, then when all seemed well, declared success and made it live.
As (bad) luck would have it, the very first real message bounced: :-(
2019-07-25 20:53:09 1hqjnY-0005ms-RD <= xxxxxxx@ntlworld.com H=cloudi.spamtitan.com [52.26.55.167] P=esmtps X=TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256 CV=no S=7854 DKIM=ntlworld.com 2019-07-25 20:53:09 1hqjnY-0005ms-RD ** mylist@lentil.org R=mailman3_router T=mailman3_t H=127.0.0.1 [127.0.0.1]: LMTP error after DATA: 550 No Message-ID header provided 2019-07-25 20:53:09 1hqjnZ-0005mx-3F <= <> R=1hqjnY-0005ms-RD U=Debian-exim P=local S=9222
The user forwarded me the bounce, which contained the original message and headers, and indeed the original message did not contain a Message-ID: header. (Oddly, his message to me reporting the error using the same mail client DID contain a Message-ID: header.)
Mail client: X-Mailer: Microsoft Outlook 16.0
So it seems in certain circumstances, Outlook doesn't put a Message-ID: header in its messages.
The change from Mailman2.x to Mailman3 means it's now using LMTP to deliver to mailman instead of a local submission seems to have exposed this issue.
Exim tries to be helpful for "locally submitted" messages:
<https://www.exim.org/exim-html-current/doc/html/spec_html/ch-message_processing.html>
"12. The Message-ID: header line
If a locally-generated or submission-mode incoming message does not contain a Message-ID: or Resent-Message-ID: header line, and the suppress_local_fixups control is not set, Exim adds a suitable header line to the message. If there are any Resent-: headers in the message, it creates Resent-Message-ID:. The id is constructed from Exim's internal message id, preceded by the letter E to ensure it starts with a letter, and followed by @ and the primary host name."
However: "Note: Messages received over TCP/IP on the loopback interface (127.0.0.1 or ::1) are not considered to be locally-originated. Exim does not treat the loopback interface specially in any way."
Therefore, Mailman3 using LMTP means exim will NOT "fix up" this problem before mailman3 receives the message.
My solution for now (apart from telling people not to use old broken Outlook!) is to modify the exim mailman3_transport so that any message with a missing Message-ID: will have one generated by exim before it's passed to LMTP. This reproduces the same behaviour exim uses for locally submitted messages.
(headers_remove ensures that we end up only with one Message-ID: header and not two, then we put back either the original Message-ID, or if that's not there, use Exim's ID to generate a new Message-ID header.)
Here's an updated version of the example at: https://mailman.readthedocs.io/en/latest/src/mailman/docs/mta.html#exim
# /etc/exim4/conf.d/main/25_mm3_macros # The colon-separated list of domains served by Mailman. domainlist mm_domains=list.example.net
MM3_LMTP_PORT=8024
# MM3_HOME must be set to mailman's var directory, wherever it is # according to your installation.
# debian default is /var/lib/mailman3 MM3_HOME=/opt/mailman/var MM3_UID=list MM3_GID=list
################################################################ # The configuration below is boilerplate: # you should not need to change it.
# The path to the list receipt (used as the required file when # matching list addresses) MM3_LISTCHK=MM3_HOME/lists/${local_part}.${domain}
# /etc/exim4/conf.d/router/455_mm3_router
mailman3_router:
driver = accept
domains = +mm_domains
require_files = MM3_LISTCHK
local_part_suffix_optional
local_part_suffix =
-bounces : -bounces+* :
-confirm : -confirm+* :
-join : -leave :
-owner : -request :
-subscribe : -unsubscribe
transport = mailman3_transport
# /etc/exim4/conf.d/transport/55_mm3_transport mailman3_transport: driver = smtp protocol = lmtp allow_localhost hosts = localhost port = MM3_LMTP_PORT rcpt_include_affixes = true
mailman3_transport: driver = smtp protocol = lmtp allow_localhost hosts = localhost port = MM3_LMTP_PORT rcpt_include_affixes = true headers_remove = message-id headers_add = "Message-ID: ${if def:header_message-id:{$h_message-id:}{<E${message_exim_id}@${qualify_domain}>}}"