Send email in WordPress over SMTP

WordPress sends every notification — password resets, new user registrations, comment alerts, contact form submissions, WooCommerce order confirmations — through one function, wp_mail(). Out of the box that function hands the message to PHP's mail(), which is why so many WordPress sites find their email silently disappearing or landing in spam. This guide routes wp_mail() through Postwing's authenticated SMTP relay instead.

Why WordPress emails do not arrive

There are two separate failures, and both are fixed by the same change:

• Nothing is listening. PHP's mail() shells out to a local sendmail binary. Most managed and cloud hosting ships without a local mail server, so the call succeeds, wp_mail() returns true, and the message is discarded.
• Nothing is authenticated. Where a local server does exist, the message leaves with no DKIM signature and from an IP that your domain's SPF record does not list. Gmail and Outlook treat that as forgery — it is filtered as spam or rejected outright.

Sending over an authenticated SMTP relay solves both: the relay signs each message with DKIM for your verified domain, and it sends from IPs your SPF record already covers, so DMARC aligns.

SMTP connection settings

Method 1 — WP Mail SMTP (recommended)

WP Mail SMTP is the most widely used option and has a built-in connection test. Install it from Plugins → Add New, then open WP Mail SMTP → Settings and fill in:

Then open the Email Test tab, send a message to yourself and confirm it arrives.

Keep the password out of the database

Entered through the settings screen, the SMTP password is stored in the WordPress database in recoverable form. Define it in wp-config.php instead — WP Mail SMTP reads these constants and greys the corresponding fields out in the UI:

/* Add ABOVE the "That's all, stop editing!" line in wp-config.php */

define( 'WPMS_ON', true );                       // let constants override the UI
define( 'WPMS_MAILER', 'smtp' );

define( 'WPMS_SMTP_HOST', 'smtp.postwing.app' );
define( 'WPMS_SMTP_PORT', 587 );
define( 'WPMS_SSL', 'tls' );                     // 'tls' = STARTTLS, 'ssl' = port 465
define( 'WPMS_SMTP_AUTH', true );
define( 'WPMS_SMTP_USER', 'token-login@your-domain.com' );
define( 'WPMS_SMTP_PASS', 'your-token-password' );

define( 'WPMS_MAIL_FROM', 'noreply@your-domain.com' );
define( 'WPMS_MAIL_FROM_NAME', 'Your Site' );
define( 'WPMS_MAIL_FROM_FORCE', true );          // override plugins that set their own From

Method 2 — FluentSMTP

FluentSMTP is free with no paid tier and supports fallback connections. Go to Settings → FluentSMTP → Add Another Connection, pick Other SMTP, and enter the same host, port 587, TLS encryption and your token credentials. Tick Store password in wp-config.php file so it is written there rather than to the database.

Method 3 — no plugin

WordPress exposes the underlying PHPMailer instance through the phpmailer_init action, so a small must-use plugin is all you need. This avoids a plugin update ever silently changing your mail setup:

<?php
/**
 * Plugin Name: SMTP for wp_mail
 * Description: Routes every wp_mail() call through an authenticated SMTP relay.
 *
 * Save as wp-content/mu-plugins/smtp-mailer.php — mu-plugins load automatically
 * and cannot be deactivated by accident from the admin.
 */

add_action( 'phpmailer_init', function ( $phpmailer ) {
    $phpmailer->isSMTP();
    $phpmailer->Host       = 'smtp.postwing.app';
    $phpmailer->Port       = 587;
    $phpmailer->SMTPSecure = 'tls';       // STARTTLS; use 'ssl' with port 465
    $phpmailer->SMTPAuth   = true;
    $phpmailer->Username   = SMTP_USER;   // defined in wp-config.php
    $phpmailer->Password   = SMTP_PASS;
    $phpmailer->Timeout    = 10;
} );

// Send as your own domain, not as wordpress@your-server-hostname
add_filter( 'wp_mail_from', fn() => 'noreply@your-domain.com' );
add_filter( 'wp_mail_from_name', fn() => 'Your Site' );

Define SMTP_USER and SMTP_PASS in wp-config.php alongside it.

Test the configuration

Each plugin has its own test button, but WP-CLI exercises the real wp_mail() path, which is what your themes and plugins actually call:

# Send a test message straight through wp_mail()
wp eval "var_dump( wp_mail( 'you@example.com', 'SMTP test', 'It works.' ) );"

# Show the underlying error if it returns false
wp eval "add_action('wp_mail_failed', fn(\$e) => print_r(\$e->get_error_message())); wp_mail('you@example.com','SMTP test','It works.');"

If it fails, log the full SMTP conversation temporarily:

// Temporarily log the SMTP conversation to debug a failing connection.
add_action( 'phpmailer_init', function ( $phpmailer ) {
    $phpmailer->SMTPDebug   = 2;
    $phpmailer->Debugoutput = 'error_log';
}, 100 );

Troubleshooting