Sympa

Sympa is a mature, open‑source mailing list manager written primarily in Perl with a rich set of C extensions for performance‑critical paths. It exposes its functionality through both a web interface (CGI/WSGI) and a SOAP API, allowing developers to integrate list management into custom workflows or third‑party services. The core engine is event‑driven: incoming mail is parsed, queued, and distributed to subscribers via SMTP or HTTP push mechanisms. Sympa’s architecture separates configuration (YAML/INI), runtime data (PostgreSQL, MySQL, or SQLite), and a lightweight cache layer (memcached or Redis) to support high‑throughput scenarios such as 20 000+ subscribers with sub‑minute delivery times.

Key Features

• Subscription & Moderation: Fine‑grained control over who can subscribe, post, or moderate; support for opt‑in/out, double‑opt‑in, and verification tokens.
• Archiving & Search: Full‑text search over archives using Apache Lucene or PostgreSQL full‑text indices; export in HTML, RSS, or raw mbox.
• Authentication: Pluggable authentication back‑ends (LDAP, PAM, HTTP Basic/Digest) and single sign‑on via OAuth2 or SAML.
• API & Webhooks: SOAP and REST endpoints for list creation, user management, and event notifications; configurable webhooks for real‑time integrations.
• Extensibility: A plugin system that lets developers hook into message flow, moderation logic, or delivery pipelines; custom scripts can be invoked via sympa CLI.

Technical Stack

The codebase is modular: core logic resides in the sympa Perl modules, while auxiliary tools (sympa, sympa-archive) are shell scripts that orchestrate the workflow. Unit tests use Perl’s Test::More, and continuous integration runs on GitHub Actions.

Deployment & Infrastructure

Sympa is intentionally lightweight: a single VM with 2 GB RAM and an SSD can comfortably host up to 10 000 subscribers, while larger deployments scale horizontally by adding more mail transport workers or database replicas. The project ships with an Ansible role (ansible-role-sympa) that automates package installation, configuration templating, and service orchestration. For containerization, a Dockerfile is available that builds a minimal image based on Alpine Linux; the image exposes ports 80/443 for the web UI and 25 for SMTP relay. Kubernetes manifests are not official but can be composed from the provided Docker image and Helm charts in community forks.

Integration & Extensibility

• Plugins: Implemented as Perl modules that hook into events such as post, pre_mod, or post_deliver. Developers can ship plugins via CPAN or local modules.
• APIs: The SOAP API (/sympa/api) supports CRUD operations on lists, users, and message queues. REST endpoints are available under /api/v1/ for lightweight integrations.
• Webhooks: Configure URLs that Sympa will POST to on events like new_subscriber, message_sent, or moderation_decision.
• Scripting: The sympa CLI allows batch operations (e.g., bulk import of subscribers) and can be scripted in Bash or Python for CI/CD pipelines.

Developer Experience

Documentation is comprehensive, with a dedicated website (https://www.sympa.community/) that covers architecture, configuration, and API reference. The community is active on GitHub Discussions and a mailing list dedicated to developers (dev@sympa.org). Licensing is GPL‑3.0, ensuring freedom to modify and redistribute. The code follows Perl best practices, with strict mode enabled by default and a consistent naming convention.

Use Cases

Advantages Over Alternatives

• Performance: Proven ability to send bulk mail to tens of thousands of recipients with minimal latency.
• Flexibility: Perl’s dynamic nature and plugin architecture allow rapid customizations without touching core code.
• Licensing: GPL‑3.0 ensures that derivative works remain open, encouraging community contributions.
• Maturity: Over a decade of production use in NGOs, universities, and large enterprises guarantees stability.
• Extensibility: SOAP/REST APIs and webhooks provide modern integration points, while the legacy CGI interface remains for backward compatibility.

In summary, Sympa offers a robust, extensible platform for developers needing a self‑hosted