Some time ago there was a discussion of threading being broken in Apple Mail. [image] Mac Mail Threading Support Yes, sigh, I know, again. 1.7 breaks the workaround we had for Mac Mail threading, namely always including “Re:” at the start of the subject Setting for email subject Re: [%{site_name}] %{optional_pm}%{topic_title} Unfortunately, Discourse 1.7 sensibly does not include an “In-Reply-To” on the first post, and this results in the first post being threaded separately from the replies in Mac Mail. I have a hack to put the “In-Reply-To” back: @message.header['Message-ID'] = incoming_mes… One of my users just reported this as having changed on our site, since we switched recently from SendGrid to Amazon SES. [image] Discourse topic openers separate from replies Site Feedback In both Mail.app and iOS Mail (latest versions), the first message in a topic (like a TidBITS article) and the replies to that topic are separate threads. Looking at the list messages I haven’t deleted, a topic started May 28 is a single thread... Reading time: 1 mins 🕑 Likes: 1 ❤ On another topic A topic-starting message from 5/31, when threading still worked contains this: Message-ID: While my message starting this topic has this: Message-ID: which doesn’t match the Message-ID references found in these headers in your reply: In-Reply-To: References: My guess this is the problem. I think all the replies remain threaded because they all contain matching References. Topic-starting messages don’t contain a References header. If Amazon SES can avoid replacing Message-IDs or if Discourse can include a self-referential References header in topic-starting messages, the problem could go away. I think this is a problem in Mail because it tries to be an old-school (proper) mail agent, using headers like this for threading, while Gmail is “dumb” and just uses the Subject. It would seem that the problem is related to the Message-ID header being different. It doesn’t seem that it’s possible to override Message-ID on SES: Amazon SES header fields - Amazon Simple Email Service Describes the header fields that Amazon SES accepts. Message-ID ( Note: Amazon SES overrides any Message-ID header you provide.) Any other thoughts about how I might be able to get threading to work for my users relying on Apple Mail (which is most of them)? @peternlewis. are you still having issues here? What email service are you sending through?

[image] adamengst: @peternlewis. are you still having issues here? What email service are you sending through? I use my own mail server (which has its own problems, but messing with the heads is not one of them).

Good to know. And using your own email server is enabling the threads to be maintained in Mail? We’ve also noticed that breaking some messages out into a new topic runs into the same problem in Mail—the new topic continues to be threaded with the old one. We’re not sure why that’s happening yet. [image] Discourse topic openers separate from replies Site Feedback I just realized “Best fonts for reading” is being threaded together with The Dark Side of Dark Mode, the topic from which it was split. The messages from the two topics sure don’t seem to share headers in common to explain this. It happens on my...

[image] adamengst: Good to know. And using your own email server is enabling the threads to be maintained in Mail? Yes. Mail threading is a bizarre black box, so “works most of the time” seems to be as good as it gets.

Threading broken in Apple Mail on the Mac and in iOS

Product Support

codinghorror (Jeff Atwood) June 19, 2019, 9:45pm 2

I believe Amazon SES messes with mail headers as I recall, in a particularly invasive way.

Ah yes I see you found that as well.

Topic		Replies	Views
Mac Mail Threading Product Support	19	2915	August 23, 2017
Threading for email-only topics seems broken Product Support	4	1407	November 9, 2017
Message threading in Mail.app Product Support	7	2407	February 9, 2016
Email threading broken Bug	7	1042	July 29, 2022
Email notifications not grouping nicely in Mail.app Feature	11	3624	October 14, 2015

Threading broken in Apple Mail on the Mac and in iOS

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