The hidden costs and security holes in Mattermost

Infrastructure and labor costs

I find that many enterprises underestimate the true price of Mattermost. While the software itself costs zero, a production server requires a dedicated cloud VM, managed PostgreSQL, and object storage from providers like AWS, DigitalOcean, or Hetzner. For a 50-person team, I calculate the total monthly cost between €4,900 and €5,700 when I account for infrastructure, labor, and compliance. A DevOps engineer in Europe costs roughly €4,200 per month for only 50 hours of work. Compliance alone adds €500 to €1,000 every month if a company operates in a GDPR-regulated environment. Management of PostgreSQL tuning, connection pooling, and SMTP relay setup is the job no one volunteers for. This labor burden is the primary reason many businesses avoid self-hosting.

The pricing for Mattermost varies by tier. The Professional tier costs $10 per user per month with an 11-user minimum. For a 50-user team, this is $500 per month. This price does not include the infrastructure costs for a cloud VM or the salary of a DevOps engineer. Companies must also handle SSL certificate renewal and regular backup verification to keep the system running.

Security vulnerabilities and data risks

Mattermost has recently faced specific security vulnerabilities that expose users to risk. In May 2026, the GitHub Advisory Database reported CVE-2026-6339, where Mattermost versions 11.5.x and 11.4.x fail to validate the X-Requested-With header on the burn-on-read reveal endpoint. This flaw allows an authenticated channel member to force the reveal of a burn-on-read message without recipient consent. Another moderate severity vulnerability, CVE-2026-6343, allows members to access public playbooks via the /get command without the necessary permissions. When a company chooses to run Mattermost on its own infrastructure, it assumes the full responsibility for managing PostgreSQL tuning, connection pooling, SMTP relay setup, SSL certificate renewal, and regular backup verification.

I see a major problem with the logic used by Massively Multi-Tenant Application vendors. These vendors use "Death Star Logic" to claim their systems are the most secure because they outspend their customers on security investments. This argument ignores the fact that hosting confidential data from thousands of enterprise customers makes these platforms prime targets for cyber attacks. In 2017, Slack reported a bug that exposed message histories and files for nearly 4 million users. A bug also left 400 million Microsoft accounts exposed to account takeover in 2018. These incidents prove that a single bug in an infrastructure can put all customers at risk. MMTA systems risk cross-bleeding your data through bugs in application logic or data layer errors. Also, these vendors become Nation State Targets because the value of breaching their system attracts the attention of hostile nations. Third-party SaaS vendors might read your data even if you use encryption because they must access unencrypted messages to perform searches. This access can be a significant problem for high-trust enterprises that require total data ownership and privacy. Can companies truly reconcile the need for total data ownership with the high cost of specialized technical labor?

Deployment choices and integration trade-offs

I find a massive gap between the cost of Slack and the cost of self-hosting Mattermost. Slack Pro costs $8.75 per user per month for 50 users, totaling $437.50 monthly. Mattermost’s Professional tier costs $10 per user per month with an 11-user minimum, making the cost $500 for a 50-user team. You probably know that Slack integrates with Salesforce and Google. Some users on Reddit prefer Mattermost because they are unhappy with using cloud platforms for sensitive network details.

Microsoft is unbundling Teams from Microsoft 365 globally to address European Commission investigations. This allows businesses to weigh whether to pay an additional $5.25 to use Teams. Slack remains an ecosystem-agnostic operator. Slack’s AI competes with Microsoft Copilot, which is backed by OpenAI’s GPT-4 model. Mattermost targets developers because it includes deep integrations with GitHub, Jira, and Bitbucket. Slack has over 2,600 integrations, while Teams has about 700.

I recommend Slack for general business teams and Mattermost for engineering departments.