RustMailer: A Self-Hosted IMAP/SMTP Middleware for Developers

Hey everyone,

I’ve been working on RustMailer for the past year, but until now I held off posting here because I felt it was missing key features and I needed to make frequent breaking changes to iterate quickly.

Today, I’m happy to announce RustMailer 1.0! 🎉

There are still a ton of things I’d like to build, but the project is now in a place where I feel more confident sharing it with the r/selfhosted community.

🌟 Key Features
🌐 Modern APIs
Offers both gRPC and OpenAPI interfaces
Multi-version API documentation
🚀 High Performance & Cost-Efficient
Written in Rust for safety and speed
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
Connection pooling for better performance
🧾 Email Template Support
Dynamic templates for transactional and marketing messages
📡 Flexible MTA Integration
Send via account-specific SMTP servers
Or use self-hosted MTA services / 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
Process them with VRL scripts for filtering and transformation
🔌 NATS Integration
Push real-time events to NATS for seamless downstream integration
🖥️ Web UI & Client
Built-in web-based email client and admin dashboard
🔐 OAuth2 Support
Built-in OAuth2 flow with web-based authorization UI
Automatically manages access & refresh tokens
🌍 Proxy Support
IMAP, SMTP, and OAuth2 proxy support for restricted environments
📦 Deployment
Single sub-60MB binary
Zero external dependencies (not even Redis)
No database required
➡ Just run it and go.
💡 License & Pricing
RustMailer is not free. A free trial is available for testing and evaluation, but production use requires purchasing a license key.

❓ Why RustMailer?
Most languages have IMAP/SMTP libraries – but they’re just low-level tools, not a production-ready email infrastructure.

To build a truly reliable email service, you need:
✓ Incremental sync (with state tracking)
✓ Battle-tested MIME parsing (BODYSTRUCTURE, encoding, attachments)
✓ SMTP with deliverability (retries, DKIM, SPF, inbox placement)
✓ Search across folders & accounts (unified search, no IMAP limits)
✓ Webhooks & event-driven tasks (idempotency, retries, scaling)
✓ Templates & batch operations (without hitting rate limits)
✓ Flaky IMAP recovery (because servers love to disconnect)

💪 What RustMailer Delivers
🚀 Massive-scale sync — 100s of accounts, zero manual management
🔍 Instant cross-account search — no IMAP roundtrips
⚡ Eventhooks API — extend functionality without modifying core logic
📦 Still just one <60MB binary — no DB, no Redis, no containers needed
If you find this useful, I’d really appreciate a ⭐ on GitHub — it helps more developers discover the project!