Rustmailer

<h1 align="center"> <img src="https://github.com/user-attachments/assets/b12d22b2-b8db-4e4c-a89f-3cd99819cedd" width="200" height="142" alt="image" /> <br> RustMailer <br> </h1> <h3 align="center"> A self-hosted Email Middleware for IMAP, SMTP, and Gmail API — built for developers </h3>

🎯 Use Cases

RustMailer is designed to be seamlessly integrated into your applications, helping you save development time and improve efficiency by providing a robust, self-hosted email synchronization and delivery backend supporting IMAP/SMTP, and Gmail API.

Typical use cases and industries include:

• SaaS platforms requiring multi-account email synchronization (IMAP or Gmail)
• CRM systems with automated transactional email sending
• Marketing automation tools supporting dynamic email templates
• Customer support software integrating real-time email notifications
• Enterprise applications needing reliable IMAP, SMTP, or Gmail API handling
• E-commerce platforms managing order confirmation and promotional emails
• Data analytics solutions tracking email opens and clicks via webhooks
• Fintech and healthcare systems demanding secure and auditable email workflows

RustMailer enables developers to focus on core application logic without building complex mail infrastructure from scratch.

<img width="1141" height="480" alt="image" src="https://github.com/user-attachments/assets/a143096b-e5d4-4966-af03-82eb53003a64" />

💡 Why RustMailer?

While many programming languages provide IMAP, SMTP, or Gmail API client libraries, building a reliable, scalable, and feature-rich mail synchronization and delivery system from scratch remains complex and time-consuming. RustMailer abstracts these challenges by offering a unified, self-hosted middleware service that:

• Handles multi-account IMAP polling and caching efficiently
• Provides robust SMTP sending capabilities with template support
• Manages event dispatch (webhooks, message queues) out of the box
• Simplifies integration across diverse application stacks regardless of language

This allows development teams to focus on core business logic, accelerating time-to-market and reducing maintenance overhead compared to assembling disparate mail client libraries individually.

✨ Features

• 🌐 Modern APIs – Offers both gRPC and OpenAPI interfaces with multi-version API documentation.
• 🚀 High Performance & Cost-Efficient – Written in Rust for safety and speed. Runs with low memory usage, no Redis or external dependencies required — ideal for production at minimal cost.
• 📬 Multi-account IMAP support – Incremental sync using UID-based strategy, supports folder selection, windowed or date-range sync.
• 📤 SMTP Sending – Manage outgoing email via SMTP with connection pooling.
• 📮 Gmail API Support – Native integration with Gmail API for account authentication, incremental synchronization, and message sending. Ideal for modern Google Workspace environments.
• 🧾 Email Template Support – Supports dynamic email templates for transactional and marketing messages.
• 📡 Flexible MTA Integration – Send via account-specific SMTP servers, self-hosted MTA services, or third-party providers.
• 📈 Open & Click Tracking – Built-in support for tracking email opens and link clicks.
• 🔄 Webhooks with VRL – Send webhook payloads to external systems and process them with VRL scripts for filtering and transformation.
• 🔌 NATS Integration – Push real-time events to NATS for seamless integration with downstream systems.
• 🖥️ Web UI & Client – Includes a built-in web-based email client and admin dashboard.
• 🔐 OAuth2 Support – Built-in OAuth2 flow with web-based authorization UI. Automatically manages access and refresh tokens.
• 🌍 Proxy Support – Supports proxies for IMAP, SMTP, and OAuth2 connections in restricted environments.

📸 Snapshot

| <img width="1548" height="861" alt="image" src="https://github.com/user-attachments/assets/46e886e5-8f17-4ab5-872e-072686e52d71" />| <img width="1552" height="741" alt="image" src="https://github.com/user-attachments/assets/054b1e1e-294e-4af0-a09a-3040552d4f90" />| |-------------------------------------|--------------------------------| | <img width="1553" height="860" alt="image" src="https://github.com/user-attachments/assets/ddd7e1a9-34dc-459b-8701-b59016b8c6e7" />| <img width="1551" height="855" alt="image" src="https://github.com/user-attachments/assets/753102d0-7df7-4efb-9099-c5beb6bf0c79" />|

API Reference

https://rustmailer.com/redoc

📦 Installation

🔧 Build from Source

To build RustMailer from source, you need the following prerequisites:

• Rust ≥ 1.88 (recommended: latest stable)
• Node.js ≥ 20
• pnpm (for building Web UI)

Step 1: Clone the repository

git clone https://github.com/rustmailer/rustmailer.git
cd rustmailer

Step 2: Build the Web UI

cd web
pnpm install
pnpm run build
cd ..

Step 3: Build the Rust backend

cargo build --release

✅ You can now run the binary from ./target/release/rustmailer.

./target/release/rustmailer --rustmailer-root-dir /tmp/data

🐳 Prefer Docker?

If you don’t want to build manually, you can follow the Docker-based installation guide here: 📄 Install via Docker

docker run -d --name rustmailer -p 15630:15630 -p 16630:16630 -e RUSTMAILER_ROOT_DIR=/data -v /sourcecode/rustmailer_data/:/data rustmailer/rustmailer:latest

🔐 RustMailer offers a free 14-day trial with unlimited email accounts during the trial period. See License for details. A valid license key is required for continued use after the trial.

⚙️ Configuration

RustMailer can be configured via environment variables or command-line arguments parsed by Clap.
The CLI configuration code is located at src/modules/settings/cli.rs.
For detailed option descriptions, please refer to the configuration reference.

# Root directory for RustMailer data storage
RUSTMAILER_ROOT_DIR=/data/rustmailer_data
# HTTP server listening port
RUSTMAILER_HTTP_PORT=15630
# Enable gRPC server
RUSTMAILER_GRPC_ENABLED=true
# gRPC server listening port
RUSTMAILER_GRPC_PORT=16630
# IP address to bind the server to (0.0.0.0 means all interfaces)
RUSTMAILER_BIND_IP=0.0.0.0
# Public URL of the RustMailer service (used in links and callbacks)
RUSTMAILER_PUBLIC_URL=http://localhost:15630
# Enable logging output to a file
RUSTMAILER_LOG_TO_FILE=true
# Enable access token authentication for API requests
RUSTMAILER_ENABLE_ACCESS_TOKEN=true

🧪 API Access

RustMailer exposes both REST (OpenAPI) and gRPC APIs for programmatic access.

You can browse all available API documentation directly via the Web UI:

🔗 OpenAPI Documentation Entry Point: http://localhost:15630/api-docs

It provides links to:

• Swagger UI: /api-docs/swagger
• ReDoc: /api-docs/redoc
• Scalar API Explorer: /api-docs/scalar
• OpenAPI Explorer: /api-docs/explorer
• OpenAPI Spec (JSON): /api-docs/spec.json
• OpenAPI Spec (YAML): /api-docs/spec.yaml

<img width="1550" height="634" alt="image" src="https://github.com/user-attachments/assets/e39d2292-200f-4eb1-bb81-224b6d979db2" />

🧠 Webhooks & NATS

RustMailer supports periodic detection of mail changes (e.g. new messages, flag updates, etc.) using scheduled scans.
It does not rely on real-time push, but instead performs full or incremental synchronization at configurable intervals.

Mail events are then emitted as:

RustMailer detects mail changes (e.g. new messages, flag updates, etc.) by periodically scanning IMAP folders.
It performs either full or incremental synchronization, depending on configuration. see details https://rustmailer.com/docs/guide/imap-sync

Detected events can be forwarded using:

• Webhooks – Supports payload transformation using VRL
• NATS Messages – Also supports VRL scripting for custom routing and filtering

🔧 Each mail account can be configured with either a webhook or a NATS sink — not both.
🌐 In addition, RustMailer supports one or more global hooks, which apply to all accounts.

<img width="1549" height="796" alt="image" src="https://github.com/user-attachments/assets/71477c2f-1ad5-4cd8-884c-6be0867007bd" />

🖥️ Web Interface

RustMailer includes a lightweight web-based mail client and admin panel, primarily designed to help developers debug and inspect synced mail content.

Accessible at:

http://localhost:15630

🔐 Web UI Access Control

• If RUSTMAILER_ENABLE_ACCESS_TOKEN=false (default), the Web UI is accessible without authentication.
• If RUSTMAILER_ENABLE_ACCESS_TOKEN=true, access is restricted to requests that provide a valid root token.

The root token file is generated at startup under the directory specified by --rustmailer-root-dir
or the RUSTMAILER_ROOT_DIR environment variable.
The token is stored in a file named: root

⚠️ The root access session expires after 5 days and requires re-authentication.

From 1.4.0, By default, the Web UI uses username/