Slack is training its machine learning features on its users' data—and everyone's opted-in by default.Slack uses machine learning, a subfield of AI, to operate in-app features like channel recommendations, search results, autocomplete, and emoji suggestions, according to the company. But it's pulling from users' Slack messages, data, and files to improve these features.Opting customers into something like AI model training by default may be frustrating for those who would have preferred advance ...