Not being able to recognize that value is not in a string

Question

I have been experimenting with Telepot to read messages in Telegram and I am trying to have the bot read a user message msg['text']. If I just print msg['text'] it echo's the user's message, so I am trying to assign it to a variable message and then have the bot reply in a certain way if a specific string was in the user's message. Whatever I input, it always prints the "Ack was found in the message" even if "Ack" or "ack" isn't in the message. I have tried further specifying by making another if statement by saying

if 'ack' or "Ack" not in message:
    bot.sendMessage(chat_id, "Ack not found") 

instead of an else, but this will just now print both if statement strings with whatever I input. Below is the full code:

import sys
import time
import telepot
from telepot.loop import MessageLoop

def handle(msg):
    content_type, chat_type, chat_id = telepot.glance(msg)
    print(content_type, chat_type, chat_id)

    message = msg['text']

    if 'ack' or "Ack" in message:
        bot.sendMessage(chat_id, "Ack was found in the messsage")

    else:
        bot.sendMessage(chat_id, "Ack not found")


MessageLoop(bot, handle).run_as_thread()
print ('Listening ...')

# Keep the program running.
while True:
    time.sleep(10)

I am following this documentation here: https://telepot.readthedocs.io/en/latest/#receive-messages

SOLUTION: Updated the code to the answer suggested by @mkrieger1

if message in {"ack","Ack"}:
    bot.sendMessage(chat_id, "Ack was found in the messsage")

if message not in {"ack","Ack"}:
    bot.sendMessage(chat_id, "Ack not found")