Discourse Emails not threaded properly in some Email clients

So being that the case most of the issues are still valid, because you are using a message-id of a message that has never been posted.

This is how I think it should be the Discourse version (changes surrounded by **asterisks**)

1) Original Post
Date: Sat, 17 Sep 2016 04:52:11 +0000
From: Paul <noreply@elixirforum.com>
Reply-To: Elixir Forum <mailserver+b4b32a98d201ecf58eef9e4c7510b978@elixirforum.com>
Message-ID: <topic/1689/10607@elixirforum.com>
**In-Reply-To: [SHOULD NOT BE PRESENT]**
**References: [SHOULD NOT BE PRESENT]**
Subject: [Elixir Forum] [Elixir Help] Semi-Manual backpressure

2) Answer to no. 1
Date: Sat, 17 Sep 2016 14:04:13 +0000
From: José Valim <noreply@elixirforum.com>
Reply-To: Elixir Forum <mailserver+81161440220741d3b07fff9c53460ba1@elixirforum.com>
Message-ID: <topic/1689/10618@elixirforum.com>
**In-Reply-To: <topic/1689/10607@elixirforum.com>**
**References: <topic/1689/10607@elixirforum.com>**
Subject: [Elixir Forum] [Elixir Help] GenStage Semi-Manual backpressure

3) Answer to no. 1
Date: Sat, 17 Sep 2016 14:59:21 +0000
From: José Valim <noreply@elixirforum.com>
Reply-To: Elixir Forum <mailserver+5a396d7011668a282e6465a58028ae8a@elixirforum.com>
Message-ID: <topic/1689/10623@elixirforum.com>
**In-Reply-To: <topic/1689/10607@elixirforum.com>**
**References: <topic/1689/10607@elixirforum.com>**
Subject: [Elixir Forum] [Elixir Help] GenStage Semi-Manual backpressure

based on the idea that topic/1689@elixirforum.com is an ID of a message that never existed (let’s call it “topic message id”)

I think there are few things causing trouble:

  • setting in the original post a “In-Reply-To” HEADER, with a reference to the non-existant topic message id.
  • setting references to a non-existant ID
  • In-Reply-To does not contain the message id of the message it’s replying to, but the non-existant topic message id, so making it impossible for some email clients to build the thread.
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