diff --git a/message/output/email/classes/event_observers.php b/message/output/email/classes/event_observers.php
new file mode 100644
index 00000000000..15a731fba9a
--- /dev/null
+++ b/message/output/email/classes/event_observers.php
@@ -0,0 +1,51 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+/**
+ * Contains an observer class containing methods for handling events.
+ *
+ * @package    message_email
+ * @copyright  2019 Mark Nelson <markn@moodle.com>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+namespace message_email;
+
+defined('MOODLE_INTERNAL') || die();
+
+/**
+ * Observer class containing methods for handling events.
+ *
+ * @package    message_email
+ * @copyright  2019 Mark Nelson <markn@moodle.com>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+class event_observers {
+
+    /**
+     * Message viewed event handler.
+     *
+     * @param \core\event\message_viewed $event The message viewed event.
+     */
+    public static function message_viewed(\core\event\message_viewed $event) {
+        global $DB;
+
+        $userid = $event->userid;
+        $messageid = $event->other['messageid'];
+
+        $DB->delete_records('message_email_messages', ['useridto' => $userid, 'messageid' => $messageid]);
+    }
+}
diff --git a/message/output/email/db/events.php b/message/output/email/db/events.php
new file mode 100644
index 00000000000..9be5277d87b
--- /dev/null
+++ b/message/output/email/db/events.php
@@ -0,0 +1,32 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+/**
+ * This file defines what events we wish to observe and the method responsible for handling the event.
+ *
+ * @package    message_email
+ * @copyright  2019 Mark Nelson <markn@moodle.com>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+defined('MOODLE_INTERNAL') || die();
+
+$observers = [
+    [
+        'eventname' => '\core\event\message_viewed',
+        'callback' => '\message_email\event_observers::message_viewed',
+    ],
+];
diff --git a/message/output/email/tests/event_observers_test.php b/message/output/email/tests/event_observers_test.php
new file mode 100644
index 00000000000..c9308cd661c
--- /dev/null
+++ b/message/output/email/tests/event_observers_test.php
@@ -0,0 +1,104 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+/**
+ * Tests the event observers.
+ *
+ * @package message_email
+ * @category test
+ * @copyright 2019 Mark Nelson <markn@moodle.com>
+ * @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+defined('MOODLE_INTERNAL') || die();
+
+/**
+ * Class for testing the event observers.
+ *
+ * @package message_email
+ * @category test
+ * @copyright 2019 Mark Nelson <markn@moodle.com>
+ * @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+class message_email_event_observers_task_testcase extends advanced_testcase {
+
+    /**
+     * Test the message viewed event observer.
+     */
+    public function test_message_viewed_observer() {
+        global $DB;
+
+        $this->preventResetByRollback(); // Messaging is not compatible with transactions.
+
+        $this->resetAfterTest();
+
+        // Create the test data.
+        $course = $this->getDataGenerator()->create_course();
+
+        $user1 = $this->getDataGenerator()->create_and_enrol($course, 'student');
+        $user2 = $this->getDataGenerator()->create_and_enrol($course, 'student');
+
+        $group1 = $this->getDataGenerator()->create_group(array('courseid' => $course->id));
+
+        groups_add_member($group1->id, $user1->id);
+        groups_add_member($group1->id, $user2->id);
+
+        $conversation = \core_message\api::create_conversation(
+            \core_message\api::MESSAGE_CONVERSATION_TYPE_GROUP,
+            [$user1->id, $user2->id],
+            'Group 1', \core_message\api::MESSAGE_CONVERSATION_ENABLED,
+            'core_group',
+            'groups',
+            $group1->id,
+            context_course::instance($course->id)->id
+        );
+
+        $message = new \core\message\message();
+        $message->courseid = 1;
+        $message->component = 'moodle';
+        $message->name = 'instantmessage';
+        $message->userfrom = $user1;
+        $message->convid = $conversation->id;
+        $message->subject = 'message subject';
+        $message->fullmessage = 'message body';
+        $message->fullmessageformat = FORMAT_MARKDOWN;
+        $message->fullmessagehtml = '<p>message body</p>';
+        $message->smallmessage = 'small message';
+        $message->notification = '0';
+
+        // Send the message twice.
+        $messageid1 = message_send($message);
+        $messageid2 = message_send($message);
+
+        // Check there are now 2 messages pending to be sent in the digest.
+        $this->assertEquals(2, $DB->count_records('message_email_messages'));
+
+        // Mark one of the messages as read.
+        $message1 = $DB->get_record('messages', ['id' => $messageid1]);
+        \core_message\api::mark_message_as_read($user2->id, $message1);
+
+        $emailmessage = $DB->get_records('message_email_messages');
+
+        // Check there is now only 1 message pending to be sent in the digest and it is the correct message.
+        $this->assertEquals(1, count($emailmessage));
+
+        $emailmessage = reset($emailmessage);
+
+        $this->assertEquals($user2->id, $emailmessage->useridto);
+        $this->assertEquals($conversation->id, $emailmessage->conversationid);
+        $this->assertEquals($messageid2, $emailmessage->messageid);
+    }
+}
diff --git a/message/output/email/version.php b/message/output/email/version.php
index aab83a52457..6fca85d4db8 100644
--- a/message/output/email/version.php
+++ b/message/output/email/version.php
@@ -24,6 +24,6 @@
 
 defined('MOODLE_INTERNAL') || die();
 
-$plugin->version   = 2019032500;        // The current plugin version (Date: YYYYMMDDXX)
+$plugin->version   = 2019042900;        // The current plugin version (Date: YYYYMMDDXX)
 $plugin->requires  = 2018112800;        // Requires this Moodle version
 $plugin->component = 'message_email';  // Full name of the plugin (used for diagnostics)