diff --git a/mod/forum/lib.php b/mod/forum/lib.php
index 36d24e6bb6d..fc81e8757b7 100644
--- a/mod/forum/lib.php
+++ b/mod/forum/lib.php
@@ -544,15 +544,15 @@ function forum_cron() {
                 }
             }
 
+            // Save the Inbound Message datakey here to reduce DB queries later.
+            $messageinboundgenerator->set_data($pid);
+            $messageinboundhandlers[$pid] = $messageinboundgenerator->fetch_data_key();
+
             // Caching subscribed users of each forum.
             if (!isset($subscribedusers[$forumid])) {
                 $modcontext = context_module::instance($coursemodules[$forumid]->id);
                 if ($subusers = \mod_forum\subscriptions::fetch_subscribed_users($forums[$forumid], 0, $modcontext, 'u.*', true)) {
 
-                    // Save the Inbound Message datakey here to reduce DB queries later.
-                    $messageinboundgenerator->set_data($pid);
-                    $messageinboundhandlers[$pid] = $messageinboundgenerator->fetch_data_key();
-
                     foreach ($subusers as $postuser) {
                         // this user is subscribed to this forum
                         $subscribedusers[$forumid][$postuser->id] = $postuser->id;
diff --git a/mod/forum/tests/mail_test.php b/mod/forum/tests/mail_test.php
index 73461079e84..db6eb94cd64 100644
--- a/mod/forum/tests/mail_test.php
+++ b/mod/forum/tests/mail_test.php
@@ -78,6 +78,23 @@ class mod_forum_mail_testcase extends advanced_testcase {
         $this->helper->mailsink->close();
     }
 
+    /**
+     * Perform message inbound setup for the mod_forum reply handler.
+     */
+    protected function helper_spoof_message_inbound_setup() {
+        global $CFG, $DB;
+        // Setup the default Inbound Message mailbox settings.
+        $CFG->messageinbound_domain = 'example.com';
+        $CFG->messageinbound_enabled = true;
+
+        // Must be no longer than 15 characters.
+        $CFG->messageinbound_mailbox = 'moodlemoodle123';
+
+        $record = $DB->get_record('messageinbound_handlers', array('classname' => '\mod_forum\message\inbound\reply_handler'));
+        $record->enabled = true;
+        $record->id = $DB->update_record('messageinbound_handlers', $record);
+    }
+
     /**
      * Helper to create the required number of users in the specified
      * course.
@@ -730,4 +747,67 @@ class mod_forum_mail_testcase extends advanced_testcase {
         // Run cron and check that the expected number of users received the notification.
         $messages = $this->helper_run_cron_check_counts($expectedmessages, $expectedcount);
     }
+
+    public function test_forum_message_inbound_multiple_posts() {
+        $this->resetAfterTest(true);
+
+        // Create a course, with a forum.
+        $course = $this->getDataGenerator()->create_course();
+        $options = array('course' => $course->id, 'forcesubscribe' => FORUM_FORCESUBSCRIBE);
+        $forum = $this->getDataGenerator()->create_module('forum', $options);
+
+        // Create a user enrolled in the course as a student.
+        list($author) = $this->helper_create_users($course, 1);
+
+        $expectedmessages = array();
+
+        // Post a discussion to the forum.
+        list($discussion, $post) = $this->helper_post_to_forum($forum, $author);
+        $this->helper_update_post_time($post, -90);
+
+        $expectedmessages[] = array(
+            'id' => $post->id,
+            'subject' => $post->subject,
+            'count' => 0,
+        );
+
+        // Then post a reply to the first discussion.
+        $reply = $this->helper_post_to_discussion($forum, $discussion, $author);
+        $this->helper_update_post_time($reply, -60);
+
+        $expectedmessages[] = array(
+            'id' => $reply->id,
+            'subject' => $reply->subject,
+            'count' => 1,
+        );
+
+        $expectedcount = 2;
+
+        // Ensure that messageinbound is enabled and configured for the forum handler.
+        $this->helper_spoof_message_inbound_setup();
+
+        $author->emailstop = '0';
+        set_user_preference('message_provider_mod_forum_posts_loggedoff', 'email', $author);
+        set_user_preference('message_provider_mod_forum_posts_loggedin', 'email', $author);
+
+        // Run cron and check that the expected number of users received the notification.
+        // Clear the mailsink, and close the messagesink.
+        $this->helper->mailsink->clear();
+        $this->helper->messagesink->close();
+
+        // Cron daily uses mtrace, turn on buffering to silence output.
+        foreach ($expectedmessages as $post) {
+            $this->expectOutputRegex("/{$post['count']} users were sent post {$post['id']}, '{$post['subject']}'/");
+        }
+
+        forum_cron();
+        $messages = $this->helper->mailsink->get_messages();
+
+        // There should be the expected number of messages.
+        $this->assertEquals($expectedcount, count($messages));
+
+        foreach ($messages as $message) {
+            $this->assertRegExp('/Reply-To: moodlemoodle123\+[^@]*@example.com/', $message->header);
+        }
+    }
 }