content: Having written chat bots that respond to keywords with prebuilt phrases, I can easily seen 39 of them able to handle a few hundred thousand people sending messages. Hell, I have a chat bot that handles a thousand customers spamming it with requests 24/7.  If you ever want to get into programming chatbots, checkout the errbot setup.  You can even have it run in a docker container with your configuration- meaning with a little work it can be running in aws/gcloud/azure very quickly and cheaply managing N number of accounts, where N is also the number of containers you have spun up.