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OwnSMTP

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Overview

Understand what OwnSMTP does, how it is designed, and when to use it.

What OwnSMTP is

OwnSMTP is an open-source HTTP-to-SMTP gateway. You run one instance with your own SMTP credentials, then your backend applications submit email through a small authenticated HTTP API.

It gives different applications one consistent integration while keeping SMTP host names, ports, passwords, and transport settings out of application code.

What it solves

  • Centralizes SMTP credentials and transport configuration.
  • Offers one JSON API across languages and frameworks.
  • Applies a local allowlist to visible sender domains.
  • Provides health and readiness endpoints for container orchestration.
  • Avoids adding a database or persistent application state.

What it does not do

OwnSMTP is not a complete SMTP server, mailbox host, marketing platform, or email provider. It does not issue SMTP credentials, maintain a delivery network, independently prove domain ownership, track opens, process bounces, or guarantee inbox delivery.

Architecture

An OwnSMTP instance is single-tenant and self-hosted: one deployment uses one SMTP configuration. It validates an incoming request and submits the resulting message to the configured relay. The service is stateless and requires no database.

Message path
Backend → OwnSMTP HTTP API → Your SMTP provider → Recipient

SMTP transport modes

  • SSL opens an encrypted connection immediately, commonly on port 465.
  • STARTTLS connects first and upgrades the connection, commonly on port 587.
  • Trusted local relay can use an unencrypted local or private connection when the relay is explicitly designed for it.

OwnSMTP versus email providers

Services such as Resend or Brevo supply email infrastructure and provider-specific APIs. OwnSMTP supplies neither. It is a gateway in your infrastructure that speaks HTTP on one side and standard SMTP on the other, so it works with any provider or local relay that gives you compatible SMTP access.