I'm a big fan of Mattermost but industry’s most flexible and secure instant messaging capabilities might be a tad exaggerated. By way of comparison, I will ind

I'm a big fan of Mattermost but industry’s most flexible and secure instant messaging capabilities might be a tad exaggerated. By way of comparison, I will indulge in a shameless plug for Webex Teams: our customers have the option of hosting their own key server, on-premise, under their control. We have no ways of seeing any content in messages: payload and title are encrypted and participants are IDs that are usually federated with their own identity provider. Decryption happens locally in the desktop/mobile client, after obtaining the right keys. Yes that's more computationally expensive and carries some complexity. But it's a very different model than just building a single big vault of data. And it also works when users in 2 different companies talk to each other, both with their own key servers. https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cloudCollaboration/spark/hybridservices/datasecurity/cmgt_b_hybrid-data-security/cmgt_b_deployment-guide-for-hybrid-data_chapter_00.html#concept_74088EF79823B0DD92298C21924E6EC3 https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cloudCol...