MQTT Q&A: What is the maximum message size in MQTT?

What is the max message size in MQTT?

An MQTT message can have a maximum size of 256 MB in a single publish. But in most cases, they are smaller than 1 MB. A common file size is less than 10 KB.

There are several reasons why it makes sense to keep messages small. One reason is, you can not retry sending a message. For example, you try to send 250 MB. At 200 MB you experience a connection abortion. This means you will have to send the whole message again.

While MQTT allows a message size up to 256 MB, many cloud providers have tight limits and do not support the maximum file size. So for professional use cases, it is important to choose your MQTT broker wisely. HiveMQ allows the configuration of a file size limit.

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