Slack does not offer end-to-end encryption, making any breach of Slack’s servers potentially catastrophic for users around the world. If you or your organization would suffer severe damage if internal Slack conversations leaked, then it’s time to consider encrypted Slack alternatives. Andrew Ford Lyons, a technologist working on digital security for at-risk groups at Internews in the UK, gives his advice. He recommends turning on mandatory two-factor authentication (2FA) and keeping Slack and email separate whenever possible.”]
Source: https://www.csoonline.com/article/3334618/4-tips-to-mitigate-slack-security-risks.html