Slack

Slack's default data center is in the United States, placing customer content under US jurisdiction and the CLOUD Act. Regional data residency, storing data at rest in locations like Frankfurt, Paris, or Singapore, is available only as an add-on for Business+ and Enterprise customers. It requires contacting Slack's sales team and can only be enabled by a Primary Owner. Free and Pro workspaces, used by most individuals and small teams, have no residency option and default to US storage.

Slack encrypts customer data at rest and in transit by default but does not offer end-to-end encryption for regular messages. Enterprise Key Management (EKM), a paid add-on available only on Enterprise Grid and Enterprise+ plans, lets organizations store their own encryption keys in AWS KMS. However, Slack's infrastructure still processes message content for search and indexing. Slack has stated it has no plans to add true end-to-end encryption.

Slack's privacy policy states that it may share personal information, including identifiers and internet activity data, with third-party advertisers for ad targeting, and that such information may be passed to corporate affiliates such as Salesforce. An independent review of the policy scored Slack's third-party data-sharing practices 24 out of 100, citing data shared with advertising partners, analytics providers, and affiliated companies.

Slack's generative AI features require opt-in consent and are not trained on customer data by default. However, its traditional machine-learning models, used for features like emoji and channel recommendations, analyze message content and usage data by default. There is no self-service toggle to stop this. The only opt-out is for a workspace or org owner to email Slack support with the subject line "Slack Global model opt-out request." This process drew public criticism in 2024 and remained unchanged as of late 2025.

Slack is closed-source, proprietary software. No source code for the client, server, or search infrastructure is published, and there is no public repository for the core product.

Slack's Trust Center lists current ISO/IEC 27001, 27017, 27018, 27701, and 42001 certifications, along with SOC 2 Type II and SOC 3 reports, covering its core platform and the GovSlack offering. These are independently audited and renewed on a recurring cycle, with compliance documentation available through Slack's Trust Center.

Slack publishes an Acceptable Use Policy governing customer conduct. Still, there is no published governance model, contributor process, or code of conduct for the product itself — development decisions are made entirely inside Salesforce.

Slack's headline pricing is a monthly per-user subscription. Pro is listed at €8.25/month standard, discounted to about €6.75/month with annual prepayment. Business+ follows the same monthly structure. There is no lifetime or one-time purchase option.

The Free plan is usable — unlimited channels, direct messages, and 1:1 huddles — but caps message history at 90 days, limits app integrations to 10, and restricts file storage to 5GB. These limits often push active teams toward a paid plan.

Slack's pricing page clearly lists each plan's features and costs. Its official downgrade instructions describe a straightforward self-service flow, from the admin billing panel to a final confirmation step, with no retention offer or hidden step along the way.

Slack's pricing page offers localized currency versions for markets including India, Japan, Brazil, and South Korea. Still, it does not publish a purchasing-power-parity methodology or a policy explaining how regional prices are set.

Self-service export on Free and Pro plans covers only public channels, with file links rather than the files themselves. Exporting private channels or direct messages, on any plan including the "self-service" tool on Business+, requires a Workspace Owner to apply, and Slack approves it only with valid legal process, member consent, or a legal requirement.

Slack offers no self-hosting option on any plan. It runs entirely as a centralized SaaS product on AWS, with no on-premises or private cloud deployments available, even to Enterprise Grid customers.

Slack requires an active, persistent connection for its core functions — sending messages, searching, and starting huddles all fail offline. The app caches recently viewed messages for read-only access, but this is not a functional offline mode.

Slack ships an official Linux desktop client in .deb, .rpm, Snap, and Flatpak formats directly from its download page, alongside Windows, macOS, iOS, and Android apps.

Slack's accessibility page mentions NVDA, JAWS, and VoiceOver screen reader support; full keyboard navigation; adjustable zoom up to 200%; reduced-motion preferences; captions and transcripts for clips and huddles; and a Simplified Layout Mode for screen-reader and switch-device users. But Slack publishes no formal WCAG conformance level, VPAT, or third-party accessibility audit to verify how completely or consistently these features are implemented across the product.

Slack has operated as a wholly owned subsidiary of Salesforce, Inc. since Salesforce's $27.7 billion acquisition closed in July 2021, Salesforce's largest acquisition to date. Salesforce is a Fortune 500 enterprise software company with a market capitalization in the hundreds of billions of dollars, and it controls Slack's roadmap, data practices, and monetization entirely.

Salesforce's acquisition of Slack closed in July 2021, more than three years before this evaluation, and there has been no further sale, merger, or change of control since. Slack has cycled through three CEOs under Salesforce ownership — Stewart Butterfield, Lidiane Jones, and Denise Dresser, who departed for OpenAI in December 2025 — but these are leadership changes, not ownership changes.

Salesforce publishes a public Ethical Use Policy and an AI Acceptable Use Policy, backed by an internal Office of Ethical & Humane Use. But in late 2025 Salesforce pitched AI hiring and case-review tools to US Immigration and Customs Enforcement, prompting over 1,400 employees to publicly demand the company drop the work, a live, unresolved conflict between the written policy and a specific commercial decision.

Salesforce reports achieving net-zero residual emissions and 100% renewable energy across its global operations, backed by a public sustainability program and annual environmental disclosure.

Slack launched publicly in August 2013 and has been continuously developed for over a decade, including under Salesforce's ownership since 2021.

Slack reported more than 10 million daily active users across more than 600,000 organizations in its 2019 IPO filing. Salesforce continues to ship active updates to the platform — new Block Kit components and AI agent tooling among them — through its public developer changelog into 2026.