Edit File: class-phpmailer.php
<?php /** * The PHPMailer class has been moved to the wp-includes/PHPMailer subdirectory and now uses the PHPMailer\PHPMailer namespace. */ if ( function_exists( '_deprecated_file' ) ) { _deprecated_file( basename( __FILE__ ), '5.5.0', WPINC . '/PHPMailer/PHPMailer.php', __( 'The PHPMailer class has been moved to wp-includes/PHPMailer subdirectory and now uses the PHPMailer\PHPMailer namespace.' ) ); } require_once __DIR__ . '/PHPMailer/PHPMailer.php'; require_once __DIR__ . '/PHPMailer/Exception.php'; class_alias( PHPMailer\PHPMailer\PHPMailer::class, 'PHPMailer' ); class_alias( PHPMailer\PHPMailer\Exception::class, 'phpmailerException' );