emqx4.3/rel/config/examples/force_shutdown.conf.example

## Force Shutdown
##
## Forced shutdown MQTT clients for overload protection

force_shutdown {
    ## set 'false' to disable force shutdown feature
    enable = true

    ## Maximum mailbox size for each Erlang process
    ## Note: Do not modify this unless you know what this is for
    max_mailbox_size = 1000

    ## Maximum heap size for each session process
    max_heap_size = 32MB
}