lib/mail/Mail.php
public function enableSandBoxMode()
    {
        if (!($this->mail_settings instanceof MailSettings)) {
            $this->mail_settings = new MailSettings();
        }
        $this->mail_settings->setSandBoxMode(true);
    }
public function enableSandBoxMode()
    {
        if (!($this->mail_settings instanceof MailSettings)) {
            $this->mail_settings = new MailSettings();
        }
        $this->mail_settings->setSandBoxMode(true);
    }
public function enableSandBoxMode ( ) { if ( ! ( $ this -> mail_settings instanceof MailSettings ) ) { $ this -> mail_settings = new MailSettings ( ) ; } $ this -> mail_settings -> setSandBoxMode ( true ) ; }
Enable sandbox mode on a MailSettings object

This allows you to send a test email to ensure that your request
body is valid and formatted correctly.
Enable sandbox mode on a MailSettings object