Merge pull request #301917 from jlian/patch-947047

Add detail about max message expiry and retained messages

Author: prmerger-automator[bot]

articles/iot-operations/manage-mqtt-broker/howto-broker-mqtt-client-options.md

@@ -6,7 +6,7 @@ ms.author: patricka
 ms.topic: how-to
 ms.service: azure-iot-operations
 ms.subservice: azure-mqtt-broker
-ms.date: 11/11/2024
+ms.date: 06/26/2025
 
 #CustomerIntent: As an operator, I want to configure an MQTT broker so that I can control MQTT client interactions.
 ---
@@ -82,7 +82,15 @@ The `maxSessionExpirySeconds` setting works with the subscriber queue limit to e
 
 Both message expiry and session expiry are important for managing slow and offline subscribers and ensuring efficient memory usage.
 
+## Max message expiry and retained Messages
+
+In MQTT 5, retained messages respect the message expiry interval specified in the `PUBLISH` packet. If an expiry interval is set, the retained message is removed once the interval elapses. If no interval is provided, the message remains available indefinitely.
+
+The `maxMessageExpirySeconds` setting defines a global upper limit for message expiry, applying to all messages, including retained ones. For example, if `maxMessageExpirySeconds` is set to `1000` seconds and a retained message specifies an expiry interval of `2000` seconds, the message is still removed after `1000` seconds.
+
+By default, `maxMessageExpirySeconds` is not set. In this case, retained messages do not expire unless an expiry interval is explicitly defined in the message.
+
 ## Related content
 
 - [Configure listeners for the MQTT broker](./howto-configure-brokerlistener.md)
-- [Test connectivity to the MQTT broker](./howto-test-connection.md)
+- [Test connectivity to the MQTT broker](./howto-test-connection.md)