Mailing list mode no longer groups properly

I have been happily using the mailing list mode since it was enabled a few weeks back. However, something seems to have changed on or around Dec 6th (yesterday) such that my mail client is now acting as if each message in a thread is its own separate thread, which makes it much harder to follow the context of a conversation.

Is anyone else seeing this behaviour change? If yes, were any configuration changes made to the Discourse instance email setup in the last few days?

If no one else is seeing this, it could be a local issue with my mail client... :sweat_smile:

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Ah, it looks like the problematic messages are using nonsensical Message-ID headers:

Date: Tue, 07 Dec 2021 08:09:36 +0000
From: "Foo via Racket Discussions" <>
Message-ID: <topic/>
Subject: [Racket Discussions] [Questions & Answers] Lazy, yet opportunistic streams
List-ID: Racket Discussions | Questions & Answers <questions-&>
Feedback-ID: racket:mailing_list:discoursemail

The Message-ID on this one references LLVM's Discourse, while all the other headers are correct... I suppose this would need to be reported upstream to Discourse somehow.

I have started a thread upstream about this.

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I've been having this issue too, but I only recently enabled Mailing list mode, so I assumed it was intentional/the default/correct (I think the option says "Send me an email for each new message" or something similar).

[This message didn't send from my email, so copied/pasted, but now time to investigate that. Anyone else use GMail to reply to messages here? Update: I need to make sure GMail replies from ben.knoble+racket, since that's the email I used here.]

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Threading for mailing list mode has now been fixed upstream. :tada:


That is good news, but I believe there will be a slight delay as the hosted discourse instances get updates every few weeks.


Golly! That was fast.