Hyvor Relay
AGPL-3.0 open-source email API for developers that can be self-hosted; supports SMTP sending, webhooks, DNS automation, observability, multi-tenancy, and project isolation.
Hyvor Relay is an open-source, self-hosted Email API designed for developers and organizations that need programmatic email sending with deliverability controls and observability. It combines a REST API backend, Go-based workers and SMTP servers, and a SvelteKit frontend to provide a complete mail delivery platform for transactional and distributional workflows.
Key Features
- RESTful, idempotent Email API that supports HTML/plain text, attachments, custom headers, and multiple recipients.
- Built-in SMTP sending components, delivery retries, greylisting handling, bounce & complaint management, and suppression lists.
- Automated DNS handling (MX/SPF/DKIM) via an integrated DNS server to simplify domain setup and signing.
- Multi-tenant projects with scoped API keys, webhooks for real-time event delivery, and 30-day searchable email logs including SMTP traces.
- Observability integrations with Prometheus metrics and Grafana dashboards, plus health checks and deliverability monitoring.
- Flexible deployment: Docker Compose / Swarm-based self-hosting, plus an enterprise licensing option with commercial support.
Use Cases
- Developers building transactional email delivery (password resets, receipts, notifications) with full control over deliverability and logs.
- Organizations wanting a self-hosted alternative to third-party providers for privacy, auditability, or regulatory reasons.
- Teams that need integrated observability and automation for large-scale sending (queue isolation, health checks, metrics).
Limitations and Considerations
- The project is licensed under AGPL-3.0; organizations that cannot accept AGPL obligations may need the commercial enterprise license option.
- The hosted "Cloud" offering was planned as a separate managed product with initial focus on transactional email; self-hosting remains the primary production path for many users.
- Hyvor Relay does not include built-in newsletter management or advanced marketing/list-management features; it targets email sending and delivery rather than full campaign management.
In summary, Hyvor Relay provides a developer-focused, open-source email sending platform with integrated DNS automation, webhooks, and observability. It is suitable for teams that need a self-hosted, extensible alternative to managed email providers while accepting AGPL licensing or opting for a commercial license.