From 1376b0ddf8e070268e154f54c78a81753bef4768 Mon Sep 17 00:00:00 2001
From: Andrew Davis <andrew@moodle.com>
Date: Wed, 14 Dec 2011 18:23:01 +0800
Subject: [PATCH 1/2] MDL-30698 forum: made message ID genuinely unique to
 prevent mail servers dropping emails the look like duplicates

---
 mod/forum/lib.php | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/mod/forum/lib.php b/mod/forum/lib.php
index f36d56e81e2..5819b43605a 100644
--- a/mod/forum/lib.php
+++ b/mod/forum/lib.php
@@ -365,6 +365,9 @@ WHERE
     return $result;
 }
 
+function forum_get_email_message_id($postid, $usertoid, $hostname) {
+    return '<moodlepost'.$postid.'to'.$usertoid.'@'.$hostname.'>';
+}
 
 /**
  * Function to be run periodically according to the moodle cron
@@ -603,14 +606,14 @@ function forum_cron() {
                            'Precedence: Bulk',
                            'List-Id: "'.$cleanforumname.'" <moodleforum'.$forum->id.'@'.$hostname.'>',
                            'List-Help: '.$CFG->wwwroot.'/mod/forum/view.php?f='.$forum->id,
-                           'Message-ID: <moodlepost'.$post->id.'@'.$hostname.'>',
+                           'Message-ID: '.forum_get_email_message_id($post->id, $userto->id, $hostname),
                            'X-Course-Id: '.$course->id,
                            'X-Course-Name: '.format_string($course->fullname, true)
                 );
 
                 if ($post->parent) {  // This post is a reply, so add headers for threading (see MDL-22551)
-                    $userfrom->customheaders[] = 'In-Reply-To: <moodlepost'.$post->parent.'@'.$hostname.'>';
-                    $userfrom->customheaders[] = 'References: <moodlepost'.$post->parent.'@'.$hostname.'>';
+                    $userfrom->customheaders[] = 'In-Reply-To: '.forum_get_email_message_id($post->parent, $userto->id, $hostname);
+                    $userfrom->customheaders[] = 'References: '.forum_get_email_message_id($post->parent, $userto->id, $hostname);
                 }
 
                 $shortname = format_string($course->shortname, true, array('context' => get_context_instance(CONTEXT_COURSE, $course->id)));

From e54816bcf8bee9505f0bfb442d9a32f6a40724dc Mon Sep 17 00:00:00 2001
From: Andrew Davis <andrew@moodle.com>
Date: Thu, 16 Feb 2012 17:08:16 +0700
Subject: [PATCH 2/2] MDL-30698 message: changed message ID to be a hash

---
 mod/forum/lib.php | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mod/forum/lib.php b/mod/forum/lib.php
index 5819b43605a..89859ef5aa2 100644
--- a/mod/forum/lib.php
+++ b/mod/forum/lib.php
@@ -366,7 +366,7 @@ WHERE
 }
 
 function forum_get_email_message_id($postid, $usertoid, $hostname) {
-    return '<moodlepost'.$postid.'to'.$usertoid.'@'.$hostname.'>';
+    return '<'.hash('sha256',$postid.'to'.$usertoid.'@'.$hostname).'>';
 }
 
 /**