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

rustmailer — Wed, 20 Aug 2025 22:07:58 +0000

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!

Why I Built RustMailer — A Self-Hosted Email Engine in Rust

rustmailer — Sat, 19 Jul 2025 15:05:17 +0000

Hi everyone 👋

I’ve been working with email protocols (IMAP, SMTP) for a while — enough to know how painful they can be when you're building something serious. A lot of tools out there either:

Don’t give you full control,
Rely on external services like Redis or heavy databases,
Or are simply too expensive to scale.

So I built RustMailer — clean, async, self-contained, and fast.

🛠 What is RustMailer?

RustMailer is a self-hosted email API engine, written in Rust, built to sync, send, and manage email with performance and reliability in mind.

No Redis. No Postgres. No cloud vendor lock-in.

It supports:

✅ Multi-account IMAP sync (UID-based, selective folders, date/window range)
✅ SMTP sending with connection pooling
✅ Webhooks powered by VRL (filter/edit payloads before sending)
✅ gRPC + OpenAPI interfaces with multi-version docs
✅ Built-in web UI for viewing messages & configuring accounts
✅ OAuth2 & proxy support for Gmail and other providers

And yes — it’s designed for real production use, not just a toy.

💰 Why RustMailer?

Because I needed something I could run cheaply, with full control, and no external dependencies.

RustMailer runs well on a small VPS with 512MB RAM and 1 CPU.

It’s source-available and requires a license only if you're using it in production beyond 10 accounts.

🤖 Built for Developers

I made RustMailer for people like me — backend developers who don’t want to rebuild email infrastructure over and over again.

If you’ve ever tried wiring together email sync, delivery, retries, webhooks, and token refresh, you know how chaotic it can get.

RustMailer handles all of that — so you can focus on building your app.

That’s it for now. I’ll write more about how it works under the hood soon (OAuth flow, sync strategy, webhook pipeline, etc).

If you have any questions or want to share your thoughts, feel free to ask in the comments — I’m happy to help and discuss!

GitHub: github.com/rustmailer/rustmailer

Website: rustmailer.com

Discord: https://discord.gg/3R4scWCsxK

DEV Community: rustmailer

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

Why I Built RustMailer — A Self-Hosted Email Engine in Rust

🛠 What is RustMailer?

💰 Why RustMailer?

🤖 Built for Developers