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. 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. The workspace would be suspended in 30 days. MidHard says Slack then deleted it, with no way to restore the history.
They looked for a way to stay, then used the deadline as the reason to leave. 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. The post warns about file-size limits and says those limits did not hit them, because large files already lived in Google Workspace.
Mattermost runs on a server they rented at Yandex Cloud. They imported the channels and accounts they needed, and they say the chats, threads, and files they needed came with them. The post does not give a skipped-channel count.
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.
Some partner workspaces stayed on Slack. The company chat moved. The external ones did not.
Their price table
They print two rounded scenarios, and they say the comparison assumes average load and no large uploads.
A team of 14 is about $126 a month on Slack and $127 self-hosted, so roughly even. A team of 40 is about $360 on Slack and $127 on Mattermost, which they call $233 a month, or about $2,800 a year. 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 same post spends a section on Mattermost’s own licensing, as they understand it. Cloud’s free tier ended in July 2023. Team Edition in v11 dropped the user cap from 1,000 to 250 and dropped GitLab SSO. The Entry plan, they write, caps history at 10,000 messages and push at 10,000 a month. Group calls, they say, cost extra after v10. Those are product limits they want you to check. They are not measurements of the MidHard import.
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.
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.