# MQTT config and general questions

**URL:** <https://discourse.nodered.org/t/mqtt-config-and-general-questions/58853>\
**Category:** General\
**Created:** [23 February 2022 01:58 UTC](https://discourse.nodered.org/t/mqtt-config-and-general-questions/58853 "2022-02-23T01:58:57Z")\
**Posts on this page:** 1\
**Showing post:** 13

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**Author:** ![Steve-Mcl](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/steve-mcl/32/4826_2.png) [@Steve-Mcl](https://discourse.nodered.org/u/Steve-Mcl)\
**Post date:** [23 February 2022 14:58 UTC](https://discourse.nodered.org/t/mqtt-config-and-general-questions/58853/13 "2022-02-23T14:58:48Z")

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> [@TotallyInformation](#):
>
> I would use v5 if I needed it 😀
> 
> Mostly you probably don't

Apart from the nifty `responseTopic` demo you did (and the [one I did](https://discourse.nodered.org/t/how-to-set-responsetopic-in-mqtt-request-message/47471/3) some time back), where V5 will be a big bonus is in the future when you have a stable running install, sending number values (not JSON) and realise you absolutely must have some additional data (like a 'timestamp' or 'gps-lat-lon' or 'device-owner') adding to the packet - however - you MUST NOT break the other 63 systems that expect a number value in the payload. This is where `User Properties` comes in very handy.

Also, another good feature you dont realise you need - until you do - is expiring retained messages. Imagine you publish every 5 mins the `fill-level` (retained) but the publisher breaks down or is offline for 6 hours - when a client connects, it will get a value that was last updated 6 hours ago. With `Expiry` set, the broker will throw the old retained message away after the specified time (probably best set to 6 minutes for this example).

Lastly, what will become more useful (in time) is the ability to auto parse the payload by checking the `Content Type` value.

Combining these feature together creates even more possibilities. e.g. suppose SERVER1 wants to send a control message to MQTTSERVER and expects a response in XML. and SERVER2 wants to send a control message to MQTTSERVER but can only handle JSON, they can both make use of the `Content Type` and `Response Topic` to ensure thats what they get.

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