Alternatives to Slack

Slack Technologies was acquired in 2021 by Salesforce, Inc., a US company headquartered in San Francisco. This subjects Slack to the CLOUD Act (2018) and the Stored Communications Act. US authorities can compel the disclosure of messages, files and metadata regardless of whether they are stored in EU data centers (Frankfurt, Dublin). The Schrems II ruling (2020) found that US surveillance laws such as FISA Section 702 conflict with the GDPR.

Slack does not provide end-to-end encryption by default. Messages are encrypted in transit (TLS) and at rest (AES-256), but Slack holds the keys. This enables server-side search, compliance exports and AI features, but it also means Slack staff, Salesforce and, under subpoena, US authorities can access content. Slack Enterprise Key Management (EKM) offers customer-controlled keys but is only available in the most expensive enterprise tiers.

Slack has changed its pricing model several times: in 2022 message history retention in the Free plan was reduced from unlimited to 90 days; in 2024 Pro pricing was raised to €8.75 per user per month (annual billing). For a team of 50 people, that is more than €5,000 per year. European alternatives such as Element (Matrix) and Olvid offer self-hosting without ongoing license fees, or unlimited retention in free tiers.

European team messengers are predominantly open source: Element is based on the Matrix protocol (Apache 2.0), Threema Libre and the Threema client code are published under AGPL, and Olvid is open source and CSPN-certified by the French cybersecurity agency ANSSI. Government agencies in France and Germany (Bundeswehr, BWI) use Matrix and Element in production. For organisations with compliance requirements, self-hosting via Matrix is an established option that is not available with Slack.