WordPress Email Log to File

email-log.php

<?php
/**
 * Plugin Name: Email Log
 * Plugin URI: https://tareq.co
 * Description: Log all outgoing emails to <code>wp-content/uploads/emails/DATE.log</code> file
 * Author: Tareq Hasan
 * Author URI: https://tareq.co
 * Version: 1.0
 */

add_filter( 'wp_mail', function( $args ) {

    $current_time = current_time( 'timestamp' );
    $upload_dir   = wp_upload_dir();
    $log_folder   = $upload_dir['basedir'] . DIRECTORY_SEPARATOR . 'emails';
    $log_file     = $log_folder . DIRECTORY_SEPARATOR . date( 'd_m_Y', $current_time ) . '.log';

    // create the emails folder if not exists
    if ( ! is_dir( $log_folder ) ) {
        mkdir( $log_folder );
    }

    $subject    = $args['subject'];
    $mail_to    = is_array( $args['to'] ) ? implode( ',', $args['to'] ) : $args['to'];
    $message    = sprintf( "[%s][%s] %s\n", date( 'h:i:s', $current_time ), $mail_to, $subject );

    error_log( $message, 3, $log_file );

    return $args;
} );