A fork of Mattermost with end-to-end encryption, custom icons, and other enhancements.

Features • Installation • Documentation • Contributing

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Overview

This fork adds several features to Mattermost that aren't available in the upstream version. All features are behind feature flags and can be enabled independently.

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Features

End-to-End Encryption

Client-side encryption using RSA-4096 + AES-256-GCM. Messages and files are encrypted in the browser before being sent to the server.

• Per-session key generation stored in sessionStorage
• Messages encrypted for all active sessions of each recipient
• File attachments encrypted with metadata hidden from server
• Purple visual styling indicates encrypted content

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Discord-Style Replies

Inline reply previews with curved connector lines, similar to Discord's reply system.

• Click Reply to queue posts, then send a message to reply to all at once
• Visual connector lines link replies to the original post
• Graceful degradation: replies appear as clickable blockquotes when disabled
• Click any reply preview to jump to the original message

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Chat Sounds

Customizable sound effects for message and reaction events, inspired by Guilded.

• Master volume control with per-sound toggles
• Sounds for: message sent, reactions, DMs, mentions, and more
• Preview buttons to test each sound
• Throttled playback to prevent audio spam

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Custom Channel Icons

Channels can have custom icons instead of the default globe/lock icons.

• Material Design Icons (7000+)
• Lucide icons
• Custom SVG via base64
• Searchable picker in channel settings

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Custom Thread Names

Threads can be renamed to something more descriptive than the first message.

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Threads in Sidebar

Followed threads appear nested under their parent channel in the sidebar.

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Hide Deleted Message Placeholders

When enabled, deleted messages disappear immediately instead of showing "(message deleted)".

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Feature Flags

Feature	Environment Variable	Default
End-to-End Encryption	MM_FEATUREFLAGS_ENCRYPTION	Off
Discord-Style Replies	MM_FEATUREFLAGS_DISCORDREPLIES	Off
Chat Sounds	MM_FEATUREFLAGS_GUILDEDSOUNDS	Off
Custom Channel Icons	MM_FEATUREFLAGS_CUSTOMCHANNELICONS	Off
Custom Thread Names	MM_FEATUREFLAGS_CUSTOMTHREADNAMES	Off
Threads in Sidebar	MM_FEATUREFLAGS_THREADSINSIDEBAR	Off
Hide Deleted Placeholders	MM_FEATUREFLAGS_HIDEDELETEDMESSAGEPLACEHOLDER	Off

Features can also be toggled in System Console > Mattermost Extended > Features:

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Installation

Building from Source

git clone https://github.com/stalecontext/mattermost-extended.git
cd mattermost-extended

# Build server
cd server && make build-linux BUILD_ENTERPRISE=false

# Build webapp
cd ../webapp && npm ci && npm run build

Creating a Release

# Commit changes, then tag and push
./build.bat 11.3.0-custom.1 "Release description"

# GitHub Actions builds and publishes automatically

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Documentation

Document	Description
Features	Detailed feature documentation
Architecture	Technical design
Build & Deploy	CI/CD and deployment
Development	Local development setup
Encryption	E2E encryption details

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Project Structure

mattermost/
├── server/
│   ├── channels/api4/               # REST API (+ encryption.go)
│   ├── channels/store/              # Database layer
│   └── public/model/                # Data models & feature flags
│
├── webapp/
│   ├── channels/src/components/     # UI components
│   ├── channels/src/utils/encryption/  # Crypto library
│   └── platform/                    # Shared packages
│
├── docs/                            # Documentation
└── .github/workflows/               # CI/CD

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Related Repositories

Repository	Description
mattermost-extended	This repository
mattermost-extended-mobile	Mobile app
mattermost-extended-cloudron-app	Cloudron packaging

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Contributing

1. Fork the repository
2. Create a feature branch
3. Test with local-test.ps1
4. Submit a pull request

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License

Licensed under the same terms as Mattermost. See LICENSE.txt.

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GitHub • Issues • Releases