What it is

Hyvor Relay is an open-source email API aimed at developers, written primarily in PHP with Symfony for the API backend and Go for the email workers, webhook handlers, DNS server, and incoming SMTP server. The frontend is built with SvelteKit and the Hyvor Design System, and PostgreSQL serves both as the database and as the queue. It lives in the PHP and Go ecosystems, is licensed under AGPL-3.0, and is positioned as a cloud and self-hosted alternative to SES, Mailgun, and SendGrid.

The concrete problem it solves is sending transactional and distributional email through your own infrastructure rather than renting deliverability from a paid provider. Hyvor Relay speaks SMTP to deliver mail, exposes a simple API for sending, and adds the operational machinery that raw SMTP lacks: queue isolation, greylisting, retry handling, bounce processing, feedback loops, and suppression management. For teams that want the control of running their own mail stack without building every deliverability safeguard from scratch, it packages those concerns into one deployable system.

Key capabilities

• Self-hosted deployment through Docker Compose or Docker Swarm, with the option of the hosted service at relay.hyvor.com.
• An email API for sending messages, backed by SMTP delivery over infrastructure you control.
• Send logs and full SMTP conversations for sent emails, retained for up to 30 days.
• Multi-tenancy with scoped access, aimed at organizations and agencies, plus multiple isolated projects inside each tenant.
• Two main queues that separate transactional from distributional email to protect IP reputation.
• Automatic greylisting and retry handling, bounce handling, feedback loop integration, and suppression management for bounces and unsubscribes.
• DNS automation through a built-in DNS server, so records do not have to be maintained by hand, alongside webhooks for email events.
• Observability through Prometheus metrics, Grafana dashboards, and logs, plus horizontal scaling by adding servers and IP addresses.
• Health checks that monitor performance and deliverability.

Who uses it and how

• Development teams that already run their own mail infrastructure and want the API, queueing, and bounce logic handled by a single self-hosted service.
• Agencies and larger organizations that need multi-tenancy, using scoped access to separate client work under one deployment.
• Product teams splitting transactional mail from bulk distribution, using the two queues so that marketing sends do not damage the reputation of the IPs carrying password resets and receipts.
• Operators who need auditability, reviewing send logs and SMTP conversations in the console when a message is delayed or rejected.
• SRE-style workflows that scrape Prometheus metrics and watch Grafana dashboards to track deliverability and queue health.

Getting started

Deploy with Docker Compose or Docker Swarm following the self-hosting documentation, or contribute against the HYVOR development environment by running ./run relay to start Hyvor Relay at https://relay.hyvor.localhost. A hosted cloud option is available at relay.hyvor.com.

When to use it — and when not to

It is the reasonable pick when the goal is to replace a paid API such as SES, Mailgun, or SendGrid while keeping delivery on your own infrastructure, though the AGPL-3.0 terms mean organizations wanting a commercial license or unwilling to comply with those terms should look at the enterprise licensing path. A self-hoster must operate PostgreSQL, which backs both the database and the queue, plus the SMTP sending path, DNS delegation, and the Prometheus and Grafana stack if observability is wanted. The project is young, with a recent first push and no listed contributors yet, so expect a smaller community and more rough edges than