Message-ID causes mail problem when sending to more than one person (e.g. forum subscription)

For this test you'll need 2 users and a course containing a forum. This test is easier if you turn down your forum maximum editing time to 1 minute (or you can check "mail now" when posting in the forum). Unless you have recently seen your Moodle send email please verify that your email sending is working. To do this check that a user's messaging preferences are set so that they receive email notifications for personal messages while both online and offline. Have another user message them within Moodle. Check that the email notification is received. This code is not affected by this bug fix. If it does not work your system is not configured correctly. Assuming that works, on to the test. You will need 2 users. Have a user subscribe to the forum (if they arent already). The subscription/unsubscription link appears in the Settings block while you are viewing the forum. Check that the user has their messaging preferences set to "email" while both online and offline for forum posts. As another user user post in the forum. Wait for your editing time to elapse. Run /admin/cron.php. Check that the subscribed user receives the notification email about the forum post. As the user who posted in the forum, post in the forum again replying to your previous post (the user is replying to themselves). Again, wait then run cron. The second notification email should be grouped by your email client.