Monte Mail Queue Throttle

A WordPress plugin that intercepts wp_mail() calls, queues eligible messages, and sends them later at a controlled pace through the configured transport.

Built for WordPress sites that send bulk mail through providers with strict rate limits, with optional Azure Communication Services Email delivery when direct provider transport is preferred.

Highlights

Current Version

0.5.0

This release adds hourly throttling, configurable worker cadence, Azure Communication Services Email delivery, test-mail support, send-window tracking, updated dashboard usage cards, and the final upload package refresh.

Architecture

Default WordPress mail flow:

WordPress or plugin -> wp_mail() -> FluentSMTP -> SMTP provider

With Monte Mail Queue Throttle:

WordPress or plugin -> wp_mail() -> Monte Mail Queue Throttle -> queued database row
WP-Cron worker -> Azure Communication Services Email REST API
WP-Cron worker -> wp_mail() replay -> FluentSMTP -> SMTP provider

When Azure transport is enabled, the worker sends directly through the Azure Communication Services Email REST API. When Azure transport is disabled, the plugin enables an internal bypass so the worker's own wp_mail() replay is not queued again.

Installation

1. Upload monte-mail-queue-throttle.zip in WordPress under Plugins > Add New > Upload Plugin.
2. Activate Monte Mail Queue Throttle.
3. Open Mail Queue > Dashboard and confirm the worker schedule is visible.
4. Open Mail Queue > Settings and review the send rate, worker interval, retry count, source mode, Azure transport settings, and retention settings.
5. If Azure delivery is enabled, add the ACS connection string and verified sender settings before sending mail.

Activation creates the queue and log tables, stores default settings when needed, and schedules the queue worker using the configured interval.

Default Behavior

Out of the box, the plugin:

• Queues all eligible wp_mail() calls.
• Processes the queue every 2 minutes with WP-Cron.
• Uses rate_per_hour = 1500.
• Uses worker_interval_minutes = 2.
• Calculates the per-run batch size from the hourly limit and worker interval.
• Retries failed messages up to 3 total attempts.
• Keeps logs for 30 days and completed sent queue rows for 180 days by default; failed queue rows are retained for at least 365 days.
• Uses exponential retry backoff before a failed message is eligible for another send attempt.
• Uses email-users,send-users-email as the default allowed plugin slug list when selected-plugin queueing is enabled.
• Falls back to normal immediate delivery if queue insertion fails.

Admin Screens

Dashboard

The plugin start screen gives administrators a clear operational overview:

• Active queue counts.
• Failed and sent totals.
• Configured mails-per-hour rate.
• Configured worker interval and calculated batch size per run.
• Next scheduled worker run.
• Stacked 30-day activity chart for queued volume plus processing, failed, and sent outcomes.
• Active queue preview with at least 10 recent queue rows when available.

Settings

Configure:

• Mails per hour.
• Worker interval minutes.
• Maximum attempts per message.
• Queue mode: all sources or selected plugins.
• Allowed plugin slugs.
• Log retention in days.
• Completed queue retention in days.
• Azure connection string.
• Verified sender domains.
• Default sender username.
• Default sender domain.
• Reply-to email.
• Test mail.

Settings are stored in the wmqt_settings option.

Queue

The queue view focuses on actionable work by default:

• Shows only queued and processing messages initially.
• Supports status filtering for other queue states.
• Uses pagination for large queues.
• Shows recipients, subject, source plugin, status, attempts, last error, queued time, and sent time.

Logs

The logs view is built for audit and diagnosis:

• Shows all events by default.
• Supports event filtering.
• Uses pagination for large log tables.
• Keeps the same related message context as the queue view.
• Includes events such as enqueue, claim, worker lock skips, throttle stops, send success, Azure provider feedback, test-mail outcomes, retry, failure, recovery, missing attachments, and encode failures.

FluentSMTP Notes

Monte Mail Queue Throttle does not replace FluentSMTP when Azure transport is disabled. In that mode, it controls when WordPress sends, then hands delivery back to the normal wp_mail() pipeline.

Configure FluentSMTP first when you want WordPress-based delivery. If Azure transport is enabled, FluentSMTP is bypassed and the worker sends through Azure Communication Services Email instead. Attachments are stored and replayed as their original local WordPress file paths, so queued payloads should be treated as trusted internal mail data.

Source Plugin Filtering

The plugin can queue either all mail or only mail from selected plugin slugs.

Source detection uses the PHP call stack and looks for files under:

wp-content/plugins/{plugin-slug}/

Known mail transport plugins such as fluent-smtp are ignored during detection so the original sender, for example send-users-email, can be recognized instead.

This detection is a throttling convenience, not a security boundary. Developers can customize ignored transport plugin slugs with:

add_filter( 'wmqt_ignored_source_plugin_slugs', function ( array $slugs ): array {
    $slugs[] = 'my-transport-plugin';
    return $slugs;
} );

GoDaddy And WP-Cron

This plugin is designed to work with managed WordPress hosting where a host or external cron calls WordPress regularly. Set Worker interval minutes to match the actual cron cadence, for example 1 when WP-Cron runs every minute.

WP-Cron normally depends on site traffic. For reliable delivery on quiet sites, make sure the host or a real server cron calls wp-cron.php regularly. If DISABLE_WP_CRON is enabled, an external cron runner is required.

If a cron request is interrupted after claiming messages, the next worker run recovers stale processing rows older than 15 minutes and returns them to queued.

Database Tables

The plugin creates two custom tables using the site's WordPress table prefix:

• {prefix}wmqt_queue
• {prefix}wmqt_logs

Deactivation clears the scheduled worker hook but keeps settings, queue rows, logs, and tables. Worker runs prune old sent queue rows according to completed queue retention; failed queue rows are kept for at least 365 days. Deleting the plugin through WordPress runs uninstall.php, which removes the plugin options, queue table, and log table.

Upload Package

The repository includes an upload-ready ZIP:

monte-mail-queue-throttle.zip

Upload that file directly through the WordPress plugin installer.

Requirements

• WordPress 5.8 or newer.
• PHP 7.1 or newer.
• A working WordPress mail transport, such as FluentSMTP.
• WP-Cron or an external cron runner.

Author

Created by Andre Essing.