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SMTP Resend Monitor

WordPress mu-plugin that monitors SMTP failures and sends alerts via Resend HTTP API. Detects failures in real-time and runs proactive health-checks every 24h.

by Mortensen · github.com/we-are-mortensen/smtp-resend-monitor

★ 0stars

Install

Download source zip No release zip yet

This is the repository archive. It installs, but the folder name will carry the branch suffix and updates will not flow.

Install straight from GitHub with WP-CLI:

wp plugin install https://github.com/we-are-mortensen/smtp-resend-monitor/archive/refs/heads/master.zip
No built-in updater. New versions won't appear under Dashboard → Updates. Install new releases yourself, or let Git Updater track the repository.
Readme github.com/we-are-mortensen/smtp-resend-monitor ↗

WordPress mu-plugin that monitors SMTP failures and sends alerts via Resend HTTP API.

The Problem

When SMTP fails on a WordPress site, there is no way to be notified — because the notification mechanism (email) is itself broken. Sites can go months with broken SMTP until someone reports that forms aren't working.

How It Works

  1. Real-time detection: Hooks into wp_mail_failed to catch SMTP failures as they happen
  2. Proactive health-check: Sends a test email every 24 hours via WP-Cron — if it fails, you get an alert
  3. Alert via HTTP: Bypasses the broken SMTP entirely by sending alerts through Resend's HTTP API
  4. Cooldown: Maximum 1 alert per 6 hours per site to prevent spam

Works with any SMTP setup: WP Mail SMTP plugin, roots/acorn-mail, or native WordPress.

Requirements

  • PHP >= 8.0
  • WordPress
  • A Resend account with a verified domain

Installation

composer require mortensen/smtp-resend-monitor

The package type is wordpress-muplugin, so Composer places it automatically in mu-plugins/.

Configuration

Add these variables to your .env file (Bedrock) or define them in wp-config.php:

Variable Required Description
SMTP_MONITOR_RESEND_API_KEY Yes Your Resend API key
SMTP_MONITOR_ALERT_TO Yes Alert recipient email
SMTP_MONITOR_ALERT_FROM Yes Alert sender email (must be from a verified Resend domain)

Bedrock (.env)

SMTP_MONITOR_RESEND_API_KEY=re_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
SMTP_MONITOR_ALERT_TO=dev@mortensen.cat
SMTP_MONITOR_ALERT_FROM=no-reply@mortensen.cat

wp-config.php

define('SMTP_MONITOR_RESEND_API_KEY', 're_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx');
define('SMTP_MONITOR_ALERT_TO', 'dev@mortensen.cat');
define('SMTP_MONITOR_ALERT_FROM', 'no-reply@mortensen.cat');

How It Detects Failures

Real-time (wp_mail_failed)

Every time wp_mail() fails, WordPress fires the wp_mail_failed action with a WP_Error object. This plugin hooks into it and sends an alert via Resend's HTTP API.

Health-check (WP-Cron)

Every 24 hours, the plugin sends a test email via wp_mail() to the site's admin email. If the send fails, it triggers an alert. This catches silent failures where no user activity triggers wp_mail().

Alert Email

You receive an email with:

  • Site name and URL
  • Error message from WordPress
  • Detection type: "Real-time" or "Health-check"
  • Timestamp

Cooldown

To prevent alert spam (e.g., a form being submitted repeatedly while SMTP is broken), only 1 alert is sent per 6 hours per site.

Behavior When Not Configured

If SMTP_MONITOR_RESEND_API_KEY is not set, the plugin does nothing — no errors, no warnings, no performance impact.

License

MIT