SMTP Connector for MailerSend releases

An independent WordPress plugin that routes every normal wp_mail() message through MailerSend SMTP. That includes WordPress core messages, Contact Form 7, and the plugin's own test message.

The plugin is intentionally focused: it configures the PHPMailer copy bundled with WordPress and does not include an API client, SDK, mail library, telemetry, advertising, or a general-purpose mail log. It can also store a Cloudflare Turnstile site key and secret key for compatible forms without implementing or calling Turnstile itself.

Features

• Authenticated STARTTLS through smtp.mailersend.net on port 2525, MailerSend's supported alternative for hosts that block port 587.
• A single mail path for core, plugin, form, and test messages.
• A quick SMTP authentication check that sends no email and stores only valid or not valid.
• Configured From email and name override unsafe sender values.
• Reply-To, CC, BCC, HTML content, message bodies, and attachments remain intact.
• The saved SMTP password is never rendered back into admin HTML.
• One sanitized diagnostic result is retained, with no message body or attachment data.
• Administrators are warned when another known mail-routing plugin is active.
• Optional Turnstile credentials are exposed through narrow WordPress filters.
• The saved Turnstile secret is never rendered back into admin HTML.
• Deactivation preserves settings; uninstall removes this plugin's options.

Requirements

• WordPress 6.5 or later
• PHP 8.1 or later
• A MailerSend account with working SMTP credentials
• A sender domain verified in MailerSend

Install

For a published version, download smtp-connector-for-mailersend.zip from the matching GitHub Release. In WordPress Admin, open Plugins > Add New Plugin > Upload Plugin, upload the ZIP, and activate it.

Existing manual installations can use the same upload screen and select Replace current with uploaded. The GitHub package retains the legacy viazen-mailersend-smtp folder inside the ZIP for this in-place upgrade path. The distribution filename, public WordPress.org slug, and translation text domain are smtp-connector-for-mailersend. Internal option names remain unchanged, so a normal replacement preserves saved credentials. Do not delete the existing plugin before replacing it because uninstall intentionally removes its options.

Then open Settings > SMTP Connector for MailerSend, enter the SMTP credentials and a verified sender, save, run Check credentials, and use Send Test Email before testing forms.

Compatible custom forms can read the optional Turnstile credentials through the viazen_mailersend_smtp_turnstile_site_key and viazen_mailersend_smtp_turnstile_secret_key filters. Both keys must be saved before a form should enable Turnstile.

For Contact Form 7, use a verified-domain address in From and put the visitor's address in Reply-To:

From:
Website Name <forms@example.com>

Reply-To:
[your-email]

Only one SMTP or mail-routing plugin should be active at a time.

Diagnostics

The settings page stores and displays only the latest WordPress mail result:

• successful handoff to the configured transport;
• SMTP authentication failure;
• SMTP connection failure;
• invalid From address;
• transport rejection; or
• general wp_mail() failure.

A successful wp_mail() result does not prove final inbox delivery. MailerSend and recipient services can still defer, filter, bounce, or reject a message later.

Development

composer install
composer check
scripts/build-release.sh

PHPStan runs at level 10 as part of composer check; the project does not use a PHPStan baseline or ignored findings.

The installable archive is written to dist/smtp-connector-for-mailersend.zip and is not committed to the source repository.

The destructive lifecycle and integration suite is intended only for a local WordPress sandbox:

WP_PATH=/opt/lampp/htdocs/sandbox scripts/test-sandbox.sh

It installs the ZIP normally, without a symlink, and verifies Plugin Check, in-place credential preservation, PHPMailer configuration, headers, diagnostics, deactivation, and uninstall.

Independent project and trademarks

This project is independently developed and maintained by @acodebeard. It is not the official MailerSend WordPress plugin and is not affiliated with, endorsed by, sponsored by, or supported by MailerSend, Inc.

MailerSend is a product of MailerSend, Inc. The MailerSend name is used only to identify the service with which this plugin interoperates. No MailerSend logo or brand artwork is included.

For MailerSend accounts, DNS authentication, service availability, billing, or delivery support, contact MailerSend. For this plugin's behavior, use this repository's GitHub Issues.

Security

Please report vulnerabilities privately as described in SECURITY.md. Do not include SMTP credentials in reports.

License

GPL-2.0-or-later. See LICENSE.