diff --git a/apps/workflowengine/lib/Check/RequestUserAgent.php b/apps/workflowengine/lib/Check/RequestUserAgent.php
index 7a8d4a71ac..4191a2f341 100644
--- a/apps/workflowengine/lib/Check/RequestUserAgent.php
+++ b/apps/workflowengine/lib/Check/RequestUserAgent.php
@@ -44,9 +44,9 @@ class RequestUserAgent extends AbstractStringCheck {
 	 * @param string $value
 	 * @return bool
 	 */
-	public function executeCheck($operator, $value)  {
+	public function executeCheck($operator, $value) {
 		$actualValue = $this->getActualValue();
-		if (in_array($operator, ['is', '!is'])) {
+		if (in_array($operator, ['is', '!is'], true)) {
 			switch ($value) {
 				case 'android':
 					$operator = $operator === 'is' ? 'matches' : '!matches';
@@ -60,6 +60,14 @@ class RequestUserAgent extends AbstractStringCheck {
 					$operator = $operator === 'is' ? 'matches' : '!matches';
 					$value = IRequest::USER_AGENT_CLIENT_DESKTOP;
 					break;
+				case 'mail':
+					if ($operator === 'is') {
+						return $this->executeStringCheck('matches', IRequest::USER_AGENT_OUTLOOK_ADDON, $actualValue)
+							|| $this->executeStringCheck('matches', IRequest::USER_AGENT_THUNDERBIRD_ADDON, $actualValue);
+					}
+
+					return $this->executeStringCheck('!matches', IRequest::USER_AGENT_OUTLOOK_ADDON, $actualValue)
+						&& $this->executeStringCheck('!matches', IRequest::USER_AGENT_THUNDERBIRD_ADDON, $actualValue);
 			}
 		}
 		return $this->executeStringCheck($operator, $value, $actualValue);
diff --git a/apps/workflowengine/tests/Check/RequestUserAgentTest.php b/apps/workflowengine/tests/Check/RequestUserAgentTest.php
new file mode 100644
index 0000000000..fe9da844cc
--- /dev/null
+++ b/apps/workflowengine/tests/Check/RequestUserAgentTest.php
@@ -0,0 +1,117 @@
+<?php
+/**
+ * @copyright Copyright (c) 2018 Joas Schilling <coding@schilljs.com>
+ *
+ * @license GNU AGPL version 3 or any later version
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program 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 Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+namespace OCA\WorkflowEngine\Tests\Check;
+
+use OCA\WorkflowEngine\Check\RequestUserAgent;
+use OCP\IL10N;
+use OCP\IRequest;
+use Test\TestCase;
+
+class RequestUserAgentTest extends TestCase {
+
+	/** @var IRequest|\PHPUnit_Framework_MockObject_MockObject */
+	protected $request;
+
+	/** @var RequestUserAgent */
+	protected $check;
+
+	public function setUp() {
+		parent::setUp();
+
+		$this->request = $this->createMock(IRequest::class);
+		/** @var IL10N|\PHPUnit_Framework_MockObject_MockObject $l */
+		$l = $this->getMockBuilder(IL10N::class)
+			->disableOriginalConstructor()
+			->getMock();
+		$l->expects($this->any())
+			->method('t')
+			->willReturnCallback(function($string, $args) {
+				return sprintf($string, $args);
+			});
+
+		$this->check = new RequestUserAgent($l, $this->request);
+	}
+
+	public function dataExecuteCheck() {
+		return [
+			['is', 'android', 'Mozilla/5.0 (Android) Nextcloud-android v2.2.0', true],
+			['is', 'android', 'Mozilla/5.0 (iOS) Nextcloud-iOS v2.2.0', false],
+			['is', 'android', 'Mozilla/5.0 (Linux) mirall/2.2.0', false],
+			['is', 'android', 'Mozilla/5.0 (Windows) Nextcloud-Outlook v2.2.0', false],
+			['is', 'android', 'Mozilla/5.0 (Linux) Nextcloud-Thunderbird v2.2.0', false],
+			['!is', 'android', 'Mozilla/5.0 (Android) Nextcloud-android v2.2.0', false],
+			['!is', 'android', 'Mozilla/5.0 (iOS) Nextcloud-iOS v2.2.0', true],
+			['!is', 'android', 'Mozilla/5.0 (Linux) mirall/2.2.0', true],
+			['!is', 'android', 'Mozilla/5.0 (Windows) Nextcloud-Outlook v2.2.0', true],
+			['!is', 'android', 'Mozilla/5.0 (Linux) Nextcloud-Thunderbird v2.2.0', true],
+
+			['is', 'ios', 'Mozilla/5.0 (Android) Nextcloud-android v2.2.0', false],
+			['is', 'ios', 'Mozilla/5.0 (iOS) Nextcloud-iOS v2.2.0', true],
+			['is', 'ios', 'Mozilla/5.0 (Linux) mirall/2.2.0', false],
+			['is', 'ios', 'Mozilla/5.0 (Windows) Nextcloud-Outlook v2.2.0', false],
+			['is', 'ios', 'Mozilla/5.0 (Linux) Nextcloud-Thunderbird v2.2.0', false],
+			['!is', 'ios', 'Mozilla/5.0 (Android) Nextcloud-android v2.2.0', true],
+			['!is', 'ios', 'Mozilla/5.0 (iOS) Nextcloud-iOS v2.2.0', false],
+			['!is', 'ios', 'Mozilla/5.0 (Linux) mirall/2.2.0', true],
+			['!is', 'ios', 'Mozilla/5.0 (Windows) Nextcloud-Outlook v2.2.0', true],
+			['!is', 'ios', 'Mozilla/5.0 (Linux) Nextcloud-Thunderbird v2.2.0', true],
+
+			['is', 'desktop', 'Mozilla/5.0 (Android) Nextcloud-android v2.2.0', false],
+			['is', 'desktop', 'Mozilla/5.0 (iOS) Nextcloud-iOS v2.2.0', false],
+			['is', 'desktop', 'Mozilla/5.0 (Linux) mirall/2.2.0', true],
+			['is', 'desktop', 'Mozilla/5.0 (Windows) Nextcloud-Outlook v2.2.0', false],
+			['is', 'desktop', 'Mozilla/5.0 (Linux) Nextcloud-Thunderbird v2.2.0', false],
+			['!is', 'desktop', 'Mozilla/5.0 (Android) Nextcloud-android v2.2.0', true],
+			['!is', 'desktop', 'Mozilla/5.0 (iOS) Nextcloud-iOS v2.2.0', true],
+			['!is', 'desktop', 'Mozilla/5.0 (Linux) mirall/2.2.0', false],
+			['!is', 'desktop', 'Mozilla/5.0 (Windows) Nextcloud-Outlook v2.2.0', true],
+			['!is', 'desktop', 'Mozilla/5.0 (Linux) Nextcloud-Thunderbird v2.2.0', true],
+
+			['is', 'mail', 'Mozilla/5.0 (Android) Nextcloud-android v2.2.0', false],
+			['is', 'mail', 'Mozilla/5.0 (iOS) Nextcloud-iOS v2.2.0', false],
+			['is', 'mail', 'Mozilla/5.0 (Linux) mirall/2.2.0', false],
+			['is', 'mail', 'Mozilla/5.0 (Windows) Nextcloud-Outlook v2.2.0', true],
+			['is', 'mail', 'Mozilla/5.0 (Linux) Nextcloud-Thunderbird v2.2.0', true],
+			['!is', 'mail', 'Mozilla/5.0 (Android) Nextcloud-android v2.2.0', true],
+			['!is', 'mail', 'Mozilla/5.0 (iOS) Nextcloud-iOS v2.2.0', true],
+			['!is', 'mail', 'Mozilla/5.0 (Linux) mirall/2.2.0', true],
+			['!is', 'mail', 'Mozilla/5.0 (Windows) Nextcloud-Outlook v2.2.0', false],
+			['!is', 'mail', 'Mozilla/5.0 (Linux) Nextcloud-Thunderbird v2.2.0', false],
+		];
+	}
+
+	/**
+	 * @dataProvider dataExecuteCheck
+	 * @param string $operation
+	 * @param string $checkValue
+	 * @param string $actualValue
+	 * @param bool $expected
+	 */
+	public function testExecuteCheck($operation, $checkValue, $actualValue, $expected) {
+		$this->request->expects($this->once())
+			->method('getHeader')
+			->willReturn($actualValue);
+
+		/** @var \OCA\WorkflowEngine\Check\AbstractStringCheck $check */
+		$this->assertEquals($expected, $this->check->executeCheck($operation, $checkValue));
+	}
+}
diff --git a/lib/public/IRequest.php b/lib/public/IRequest.php
index b313020711..05948cd480 100644
--- a/lib/public/IRequest.php
+++ b/lib/public/IRequest.php
@@ -90,6 +90,16 @@ interface IRequest {
 	 */
 	const USER_AGENT_TALK_IOS = '/^Mozilla\/5\.0 \(iOS\) Nextcloud\-Talk v.*$/';
 
+	/**
+	 * @since 13.0.1
+	 */
+	const USER_AGENT_OUTLOOK_ADDON = '/^Mozilla\/5\.0 \([A-Za-z ]+\) Nextcloud\-Outlook v.*$/';
+
+	/**
+	 * @since 13.0.1
+	 */
+	const USER_AGENT_THUNDERBIRD_ADDON = '/^Mozilla\/5\.0 \([A-Za-z ]+\) Nextcloud\-Thunderbird v.*$/';
+
 	/**
 	 * @param string $name
 	 *