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Postal API Connector for FluentSMTP

A simple connector to extend FluentSMTP to use the API to connect to the PostalSMTP server.

by One Dog Solutions · github.com/onedogsolutions/fluentsmtp-to-postalsmtp · website

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Install

No release zip yet. The repository archive installs, but the folder name will carry the branch suffix and updates will not flow:

wp plugin install https://github.com/onedogsolutions/fluentsmtp-to-postalsmtp/archive/refs/heads/main.zip
Readme github.com/onedogsolutions/fluentsmtp-to-postalsmtp ↗

A companion WordPress plugin that adds a Postal connection to FluentSMTP, delivering WordPress mail through a self-hosted Postal server's HTTP API (POST /api/v1/send/raw) instead of SMTP.

📣 Shoutout to Jewel at WPManageNinja! 👋 We'd love to see Postal supported natively in FluentSMTP — please consider merging this into core ASAP. It was built specifically to mirror FluentSMTP's own structure, so adopting it is mostly moving files: the drop-in provider Handler, ValidatorTrait, and Postal.vue are ready to go. See merge/README.md for the exact steps. Thanks, friend! 🙏

Why

Self-hosted Postal servers usually sit behind a reverse proxy (Caddy, nginx) with a valid Let's Encrypt certificate on port 443, while the SMTP submission ports (465/587) have historically been harder to secure — older Postal versions have STARTTLS/certificate problems there. This connector sends over the already-valid HTTPS API endpoint using a scoped, revocable server API key, so it sidesteps the SMTP TLS stack entirely while keeping delivery on your own infrastructure.

Because PHPMailer's fully-assembled MIME message is delivered via /api/v1/send/raw, multipart bodies, inline images, attachments, custom headers and DKIM-relevant structure are transmitted byte-for-byte — exactly what SMTP would have carried.

Requirements

  • WordPress 5.5+
  • PHP 7.4+
  • The FluentSMTP plugin, installed and active
  • A Postal server with an API credential (Server → Credentials → New Credential → type API) and a verified sending domain

Installation

  1. Install and activate FluentSMTP.
  2. Install and activate this plugin.
  3. Go to Settings → Postal (FluentSMTP) and add a connection:
    • Postal Server URL — e.g. https://postal.example.com
    • Server API Key — the API credential from your Postal server
    • From Email / Name — a sender on a domain verified in Postal
  4. Click Test Connection, then Save. Use Send Test to send a real email through Postal.

Saved connections appear in FluentSMTP and are used automatically for matching From addresses, including FluentSMTP's email logging, fallback connections and resend-from-log.

Storing the API key in wp-config.php (optional)

Instead of the database, choose "Store API Keys in Config File" and add:

define( 'FLUENTSMTP_POSTAL_API_KEY', 'your-postal-api-key' );

When stored in the database, the key is encrypted at rest using your WordPress security keys (requires the OpenSSL PHP extension).

Security notes

  • Delivery is over HTTPS to the URL you configure; the API key is sent only in the X-Server-API-Key header.
  • Verify SSL Certificate is on by default. Only disable it for self-signed certificates on isolated lab servers — the connection stays encrypted but is no longer authenticated.
  • The sending domain must be verified on your Postal server, otherwise Postal rejects the message as an unauthenticated From address.

Development

The admin setup screen is a Vue 2 + Element UI app built with Laravel Mix, using the same stack and component conventions as FluentSMTP so the provider form can be merged upstream.

npm install
npm run prod      # build assets/ (committed)
npm run watch     # develop
composer install  # dev-only: PHP lint / phpcs

The compiled bundle in assets/ is committed so the plugin runs on install.

Upstream merge

This connector is structured so FluentSMTP's maintainers can adopt Postal as a first-class provider with mostly file moves. See merge/README.md.

License

GPL-2.0-or-later.