MidHard Games published this on 5 March 2026. The team says the work happened in January 2026. Slack had been the company chat since 2016, more than nine years. The workspace had 266 users, and 98 of them were active at the peak.
On 19 December 2025 Slack emailed them. The letter they quote says Slack has to follow US, EU, and other sanctions rules. Their account was based in Russia, or mostly used there, or otherwise connected to distribution there. The workspace would be suspended in 30 days. MidHard says Slack then deleted it, with no way to restore the history. They do not publish Slack’s deletion notice, only that outcome.
They looked for a way to stay, then used the deadline as the reason to leave. The goal they write down is a replacement that keeps the working habits and costs less. The Slack → Mattermost playbook assumes you still have a paid export. With a 30-day clock, that export is the first afternoon.
What they carried, and what they rebuilt
They exported with slackdump. Builds and source are both available, they say. The post warns about file-size limits and says those limits did not hit them, because large files already lived in Google Workspace. They also say the tool has nuances, and that they reworked the export until it matched what they wanted. They point at Mattermost’s export docs for that part. There is no skipped-channel count.
Mattermost runs on a server they rented at Yandex Cloud, after they looked at other hosts. No instance size is on the page. They imported the channels and accounts they needed, and they say the chats, threads, and files they needed came with them.
Calls were a separate hole. Mattermost has no calls app built in. In 2025 Slack calls had already been unreliable for them on one carrier, and they had been falling back to Telemost. On Mattermost they wired calls through Jitsi, and document preview through Collabora. The “huddle” button they missed in Slack is the thing Jitsi is standing in for.
Some partner workspaces stayed on Slack. The company chat moved. The external ones did not. Leaving Slack entirely was not available while those partners still used it.
Their price table
They print two rounded scenarios, and they say the comparison assumes average load and no large uploads.
| Team | Slack / month | Self-hosted Mattermost / month | Their difference |
|---|---|---|---|
| 14 people | $126 | $127 | about even, $1 the other way |
| 40 people | $360 | $127 | $233 / month, about $2,800 / year |
The self-hosted column does not change with the headcount. That is why they say a larger team pays less per person. They also project $25,000 or more over the next nine years. That last number is a forecast, not a bill they have paid. The $127 is the same in both rows, so the nine-year figure depends on which team size you hold still, and they do not show the arithmetic.
You maintain the server. They already run machines in more than one data center, so they treated that as normal work. If you do not, the $127 line is not the whole cost. They also say the self-hosted box gave them more control than they had expected. They decline to describe the setup, and they tell you to take that on their word.
The license limits, checked against Mattermost
The same post spends a section on Mattermost’s licensing, as they understand it. Those notes are not measurements of the MidHard import. They also do not say which edition they installed. Mattermost’s own pages sharpen a few of the lines.
Cloud’s free tier ended on a date. Mattermost’s April 2023 notice says Cloud Free would no longer be offered after 26 July 2023, for new and existing workspaces. MidHard’s “July 2023” matches that month. The notice points self-hosting, or a paid cloud plan, at the people who were on it.
Team Edition is the MIT-compiled build. Mattermost’s v11 forum post says that in v11 the user limit drops from 1,000 to 250, and GitLab SSO comes out. MidHard has both of those. The editions page describes Team Edition as the option under 250 activated users when you do not need SSO.
Entry is the other free option, a commercial license rather than the open-source build. MidHard writes a ceiling of 50 people, a history cap of 10,000 messages, and 10,000 push notifications a month. Mattermost’s pages describe Entry as the fit for teams of about 25 to 50, and they print the same 10,000 message and 10,000 push caps. The editions page marks several of those caps, including calls, as limits that take effect in a future release. MidHard presents them as current.
The call lines do not match cleanly. MidHard says a call duration limit of up to 40 minutes. Mattermost’s Entry announcement says 1:1 audio calls are limited to 40 minutes. The post also says that in v10 the Calls plugin stayed free for direct messages, and that group calls in channels moved to a paid subscription at $10 per user per month, with a Reddit thread as the pointer. That price is not on the edition pages cited above. It stays MidHard’s reading of that thread.
The post adds that the shared codebase lets you build your own version and turn features back on. That is their closing option, not a build they say they shipped.
Export on the day the letter arrives. Thirty days is the window they were given, and they say the workspace was deleted after it. Keep a copy of the export even after the import looks done. Partner Slack workspaces will still be there on Monday. The playbook is how the file becomes Mattermost posts, once you still have the file.