Mattermost Mission Collaboration for Microsoft is a plugin that embeds Mattermost directly inside Microsoft 365, Teams, and Outlook clients. This integration extends Microsoft 365, Teams, and Outlook for mission-critical coordination, command and control, incident response, and DevSecOps workflows in demanding environments, including air-gapped and classified networks.

Benefits & Use Cases:

• External Collaboration with IT Control: Replace non-compliant freemium personal apps with dedicated external collaboration across mobile, web, and desktop, fully controlled by IT.
• Intelligent, AI-Accelerated Incident Response: Augment Microsoft Security Suite with AI-powered collaborative workflows, from detection to resolution, within secure environments.
• Sovereign, Cyber-Resilient S4B Replacement for Classified Workflows: Replace legacy Skype for Business with a self-hosted, fully sovereign solution for classified operations, tightly integrated within Microsoft ecosystems.
• Embedded DevSecOps Collaboration Inside Microsoft Teams: Maintain a unified user experience while achieving higher operational productivity for DevSecOps and mission teams.
• Mission Operations at the Tactical Edge: Real-time command and control for joint operations, mission partner environments, and disconnected/denied environments (DDIL).

Features:

• Direct Access: Access Mattermost directly from a tab without switching applications or opening a browser.
• Seamless Integration: Experience the full functionality of Mattermost within a familiar Microsoft Teams interface.
• Real-time Collaboration: Collaborate with your team on projects, workflows, and communications in real time.
• Unified Communications: Combine chat, meetings, workflows, and task management inside MS Teams.
• Secure Data Handling: Maintain data sovereignty with self-hosted deployment options.
• AI-Powered Insights: Use multi-agent AI, including Azure OpenAI and local LLMs, for faster decision-making and situational awareness.
• Embedded DevSecOps Collaboration: Keep developer teams productive with integrated workflows inside Microsoft Teams.
• Entra-Based SSO: Simplify user authentication and enhance security with enterprise-grade identity management for organizations using Microsoft Entra ID.
• Activity Feed Notifications for Mentions in Mattermost: Never miss critical updates, with real-time notifications in your MS Teams activity feed whenever someone mentions you in Mattermost.

This app is designed to work with Microsoft 365, Outlook, and Microsoft Teams.

For detailed setup instructions, see the Setup Guide, which provides step-by-step instructions for creating and configuring a Microsoft Teams application in Azure, setting up the Mattermost plugin, and installing Mattermost in Microsoft Teams.

You can browse existing open issues or submit a new issue for support in GitHub: https://github.com/mattermost/mattermost-teams-tab/issues

If after following the Setup Guide, you see a 404 error in the MS Teams tab, it likely means the plugin did not start correctly on your Mattermost instance. Check the plugin configuration for any missing or incorrect settings. Also ensure the Site URL is correct and reachable for your Mattermost instance.

If after following the Setup Guide, your users cannot see the M365 app uploaded to your app store, you may simply need to wait. Microsoft states this can take up to 24 hours, however our experience has been the delay is anywhere from seconds to a few hours. If after 24 hours users still cannot see the app, you may need to remove it and upload it again.

This is likely due to re-installing the app in your app store, and a new internal ID being generated. Restarting the plugin in Mattermost will resolve this.

Outlook for Mac (native client) does not support apps currently. MS Teams on Mac (native client) is supported as are web clients for Outlook, MS Teams and Microsoft 365.

The appstore/ directory contains one subdirectory per Teams app store submission (Community for Mattermost, Corpus, HUB). Each follows this layout:

appstore/<AppName>/
  assets/            # Source images — edit these; never commit directly as submission icons
    logo-color.png   # Full-resolution color source (any size, square)
    logo-outline.png # Full-resolution outline source (any size, square)
  marketplace/       # Store screenshots (not included in submission zip)
  logo-color.png     # Generated 192×192 color icon — committed, bundled
  logo-outline.png   # Generated 32×32 outline icon — committed, bundled
  manifest.json      # Teams app manifest — bundled

After editing any file under assets/, regenerate and commit the submission icons:

make appstore-icons   # requires sips (macOS) or ImageMagick (magick/convert)
git add appstore/*/logo-*.png
git commit -m "Regenerate appstore icons"

make appstore-bundles   # requires jq; produces dist/appstore/<AppName>-<version>.zip

Each zip contains only manifest.json, logo-color.png, and logo-outline.png. The assets/, marketplace/, and .DS_Store files are excluded automatically.

Run /appstore-review in Claude Code to fetch the current Microsoft Teams Store guidelines and validate every app package against them.