こちらで作成したブローカーに接続する方法です。
Mosquitto で Let's Encrypt の証明書を使う

.env

HOST=abc.example.com
TOPIC=sensors/topic_1

publish_ca.py

# ! /usr/bin/python
# -*- coding: utf-8 -*-
#
#	publish_ca.py
#
#					Jan/23/2021
#
# ------------------------------------------------------------------
import	sys
import	os
from dotenv import load_dotenv
from time import sleep
import paho.mqtt.client as mqtt

# ------------------------------------------------------------------
sys.stderr.write("*** 開始 ***\n")
dotenv_path = '.env'
load_dotenv(dotenv_path)
host = os.environ.get("HOST")
topic = os.environ.get("TOPIC")

port = 8883

client = mqtt.Client(protocol=mqtt.MQTTv311)
client.tls_set('/etc/ssl/certs/ca-certificates.crt')

client.connect(host, port=port, keepalive=60)

client.publish(topic, 'Good Afternoon')
sleep(0.5)
client.publish(topic, 'こんにちは')

client.disconnect()

sys.stderr.write("*** 終了 ***\n")
# ------------------------------------------------------------------

subscribe_ca.py

# ! /usr/bin/python
# -*- coding: utf-8 -*-
#
#	subscribe_ca.py
#
#					Jan/23/2021
#
# ------------------------------------------------------------------
import	sys
import	os
from dotenv import load_dotenv
from time import sleep
import paho.mqtt.client as mqtt

# ------------------------------------------------------------------
def on_connect(client, userdata, flags, respons_code):
	print('status {0}'.format(respons_code))

	client.subscribe(topic)

def on_message(client, userdata, msg):
	print(msg.topic + ' ' + str(msg.payload,'utf-8'))

# ------------------------------------------------------------------
sys.stderr.write("*** 開始 ***\n")

dotenv_path = '.env'
load_dotenv(dotenv_path)
host = os.environ.get("HOST")
topic = os.environ.get("TOPIC")
port = 8883

client = mqtt.Client(protocol=mqtt.MQTTv311)
client.tls_set('/etc/ssl/certs/ca-certificates.crt')

client.on_connect = on_connect
client.on_message = on_message

client.connect(host, port=port, keepalive=60)

client.loop_forever()

sys.stderr.write("*** 終了 ***\n")
# ------------------------------------------------------------------