A sales rep in Singapore pastes a prospect's full credit card number into #deals. A team lead in Jakarta forwards an entire customer contract to a public Slack channel by mistake. An intern in Manila screenshots a client's bank details and drops it in #general. These aren't edge cases. They happen because most team chat tools—Slack, Teams, Lark—were designed for internal coordination, not customer data handling. Once data lands in a channel, it's searchable, archived, and accessible to anyone with channel access. One wrong permission setting and sensitive information spreads across your entire team. We tested this with a real 8-person sales team across Singapore, Jakarta, and Manila. We ran the same workflows—prospect lookups, contract sharing, payment collection, customer follow-ups—through Slack, Teams, Lark, and Orin. The results show why most teams either leak customer data or create so many permission silos they kill productivity. The core problem: chat tools are not CRM-aware When your team chat is separate from your CRM, customer data has to move between two systems. That's where leaks happen. Slack, Teams, and Lark all have the same fundamental architecture: channels are either public (searchable by anyone in your workspace) or private (searchable by channel members). Once something is posted, it's indexed and stored indefinitely—unless you manually delete it or set a strict retention policy that actually gets enforced. Here's what we saw in practice: Prospect lookups: Sales reps copy-pasted customer email, phone, and company details into #prospects to get quick feedback. In Slack and Teams, this data lived in the channel history forever. Lark has similar retention but better keyword-filtering for deletion. No tool prevented the copy-paste in the first place. Contract negotiation: Reps shared PDF contracts in private channels for manager review. The problem: channel membership often expanded (new hires, consultants) but nobody removed old members. We found contracts from 2023 still searchable by people who'd left the deals. Payment details: One team member set up a shared channel for "payment follow-ups." It became a dumping ground for invoice PDFs, partial card numbers (last 4 digits + customer name), and bank account screenshots. All searchable. All permanent unless manually purged. Customer support context: Support reps dropped customer chat transcripts into channels to ask sales for context. Raw customer messages—complaint details, account numbers, screenshots of errors—now lived in indexed channel history. None of these workflows are wrong on their own. But none of the standard chat tools have a permission model that prevents data leakage while keeping collaboration fast. Slack: Powerful search, permanent retention, weak data boundaries Slack is the most widely used team chat tool, and its strength is also its weakness: everything is searchable and retrievable. Permission model: Slack distinguishes between public channels (anyone can join and search), private channels (invite-only, but members can search), and direct messages (2-person, not searchable by others). You can restrict channel creation and set workspace-wide retention policies, but once data is in a channel, access is binary: either you're in it or you're not. In our test, this meant: We created a #customer-data channel thinking it would be "restricted." It wasn't—any new team member could ask to join and see all historical customer records. We set a 90-day retention policy on Slack Pro, but it only auto-deletes messages. Customer data shared as PDFs, image files, or in threads often wasn't caught by the purge. Slack's "data loss prevention" (DLP) features require Enterprise tier and only scan message content, not attachments or links to external files. The real friction: To keep customer data out of Slack, your team has to use external links (Notion, Google Drive, etc.) instead of pasting data directly. But then you lose the speed of in-chat collaboration, and you can't control who downloads or screenshots the file. Teams: Similar structure, better encryption, still searchable Microsoft Teams has the same channel-based architecture as Slack, with slightly stricter controls but the same fundamental problem. Permission model: Teams distinguishes between standard channels (more open) and private channels (invite-only). It integrates with Azure AD, so you can enforce conditional access policies and require multi-factor authentication. Retention policies are more granular than Slack—you can set different rules for different channels. What we found: Teams' Azure integration made it easier to revoke access when someone left the company. Slack requires manual removal from channels; Teams can do it at the workspace level. Teams' retention policies are more reliable than Slack's. We set a 30-day auto-deletion policy on a test channel, and it actually worked—files and messages were purged on schedule. But Teams still has the same core issue: o