WordPress Email Logger (works for single site and multisite)

wp-email-logger.php

<?php
/**
 * Plugin Name: Email Logger
 * Description: Logs all emails sent from WordPress (works for single site and multisite)
 * Network: true
 */

add_filter('wp_mail', 'universal_log_wp_mail', 999);
function universal_log_wp_mail($args) {
    $is_multisite = is_multisite();
    $option_key = $is_multisite ? 'network_emails_log' : 'emails_log';
    
    // Get existing emails
    $emails = $is_multisite ? get_site_option($option_key, array()) : get_option($option_key, array());
    
    $email_data = array(
        'time' => current_time('mysql'),
        'to' => $args['to'],
        'subject' => $args['subject'],
        'message' => $args['message'],
        'headers' => $args['headers'] ?? '',
    );
    
    // Add site_id for multisite
    if ($is_multisite) {
        $email_data['site_id'] = get_current_blog_id();
    }
    
    // Keep last 50 emails
    array_unshift($emails, $email_data);
    $emails = array_slice($emails, 0, 50);
    
    // Update option
    if ($is_multisite) {
        update_site_option($option_key, $emails);
    } else {
        update_option($option_key, $emails);
    }
    
    return $args;
}

// Add admin menu for both single site and multisite
if (is_multisite()) {
    add_action('network_admin_menu', 'universal_email_log_menu');
} else {
    add_action('admin_menu', 'universal_email_log_menu');
}

function universal_email_log_menu() {
    $is_multisite = is_multisite();
    $capability = $is_multisite ? 'manage_network' : 'manage_options';
    
    add_menu_page(
        'Email Log',
        'Email Log',
        $capability,
        'email-log',
        'universal_email_log_page',
        'dashicons-email'
    );
}

function universal_email_log_page() {
    $is_multisite = is_multisite();
    $option_key = $is_multisite ? 'network_emails_log' : 'emails_log';
    $emails = $is_multisite ? get_site_option($option_key, array()) : get_option($option_key, array());
    
    echo '<div class="wrap">';
    echo '<h1>' . ($is_multisite ? 'Network ' : '') . 'Email Log</h1>';
    
    if (isset($_POST['clear_log'])) {
        check_admin_referer('clear_email_log');
        
        if ($is_multisite) {
            delete_site_option($option_key);
        } else {
            delete_option($option_key);
        }
        
        echo '<div class="notice notice-success"><p>Email log cleared!</p></div>';
        $emails = array();
    }
    
    echo '<form method="post" style="margin-bottom: 20px;">';
    wp_nonce_field('clear_email_log');
    echo '<input type="submit" name="clear_log" class="button" value="Clear Log">';
    echo '</form>';
    
    if (empty($emails)) {
        echo '<p>No emails logged yet.</p>';
    } else {
        foreach ($emails as $email) {
            echo '<div style="border: 1px solid #ccc; padding: 15px; margin-bottom: 20px; background: #f9f9f9;">';
            echo '<p><strong>Time:</strong> ' . esc_html($email['time']) . '</p>';
            
            // Show site ID only for multisite
            if ($is_multisite && isset($email['site_id'])) {
                echo '<p><strong>Site ID:</strong> ' . esc_html($email['site_id']) . '</p>';
            }
            
            echo '<p><strong>To:</strong> ' . esc_html(is_array($email['to']) ? implode(', ', $email['to']) : $email['to']) . '</p>';
            echo '<p><strong>Subject:</strong> ' . esc_html($email['subject']) . '</p>';
            echo '<p><strong>Message:</strong></p>';
            echo '<pre style="background: white; padding: 10px; overflow-x: auto;">' . esc_html($email['message']) . '</pre>';
            echo '</div>';
        }
    }
    
    echo '</div>';
}