WildDuck Mail Server

WildDuck is a high‑performance, horizontally scalable IMAP/POP3 mail server written in Node.js. It stores every piece of mailbox data—users, folders, messages and metadata—in a sharded‑replicated MongoDB cluster. This design eliminates the single‑point‑of‑failure typical of traditional MTA/Dovecot stacks and allows a developer to add or remove nodes without downtime. The server exposes a RESTful JSON API that mirrors the full set of IMAP commands, making it trivial to integrate with webmail clients, mobile apps or custom tooling.

Architecture

• Runtime: Node.js (v18+), leveraging asynchronous I/O for low latency.
• Database Layer: MongoDB (sharded + replica sets). Each mailbox is a collection of documents; message bodies are stored as GridFS objects, while headers and flags reside in the main collection.
• API Layer: Express‑like router that auto‑generates OpenAPI 3.0 docs (openapidocs.json). The API is stateless and supports pagination, filtering, and WebSocket push for real‑time updates.
• Email Delivery: Designed to be paired with Haraka or ZoneMTA; WildDuck itself does not send mail, only receives via SMTP (via the partner MTA) and serves it to clients.
• Extensibility: Hooks for custom authentication (JWT, LDAP), rate limiting, and message hooks (e.g., virus scanning) are exposed through middleware.

Core Capabilities

• Full IMAP/POP3 compliance: Supports UID, EXISTS, FETCH, STORE, COPY, EXPUNGE, and all modern extensions (e.g., IMAP IDLE, QUOTA, UIDPLUS).
• Unicode‑first: Handles UTF‑8 mailbox names and email addresses without workarounds.
• API‑driven configuration: Users, mailboxes, quotas and ACLs can be created, updated or deleted via HTTP calls—no need for dovecot.conf‑style files.
• Message Search: Full‑text search powered by MongoDB’s text indexes, enabling fast keyword queries across all messages.
• Webhooks: Clients can subscribe to mailbox events (new message, flag change) via WebSocket or HTTP callbacks.

Deployment & Infrastructure

• Container‑friendly: Official Docker images are available; the server can be run behind a reverse proxy (NGINX, Traefik) with TLS termination.
• Horizontal scaling: Add MongoDB shards or node instances behind a load balancer; the API is stateless, so any instance can serve any request.
• Self‑hosted prerequisites: Node.js runtime, a MongoDB cluster (or single node for testing), and an SMTP relay such as Haraka or ZoneMTA.
• Monitoring: Exposes Prometheus metrics (/metrics) and supports OpenTelemetry tracing.

Integration & Extensibility

• Plugin system: Custom middleware can be injected into the request pipeline to implement Sieve-like filtering, DKIM signing or custom authentication.
• SDKs: Official JavaScript client libraries simplify consuming the REST API; community has bindings for Python, Go and others.
• Webhooks & Callbacks: External services can react to mailbox changes in real time, enabling mail‑based workflows (e.g., ticketing systems).
• Custom UI: The React‑based webmail demo can be forked; developers can replace it with any front end that talks to the API.

Developer Experience

• Documentation: Comprehensive docs (docs.wildduck.email) cover API usage, authentication flows, and deployment scenarios. The OpenAPI spec is machine‑readable for auto‑generation of SDKs.
• Community: Active Gitter channel, GitHub issues, and a permissive EU‑Public license encourage contributions.
• Configuration: Environment variables control all runtime parameters—no complex config files, making CI/CD pipelines straightforward.

Use Cases

• Enterprise mail hosting: 1 000+ accounts with large per‑user quotas, requiring horizontal scaling and zero downtime.
• Custom mail clients: Mobile or web apps that need a lightweight backend; the REST API removes the need for IMAP libraries on the client side.
• Mail‑based automation: Integrate with CI/CD pipelines or ticketing systems where email triggers actions via webhooks.
• Hybrid deployments: Combine WildDuck with Haraka/ZoneMTA to replace Dovecot while keeping existing SMTP infrastructure.

Advantages Over Alternatives

For developers prioritizing scalability, API‑driven workflows and a modern JavaScript ecosystem, WildDuck offers a compelling alternative to legacy MTA/Dovecot stacks.