Проверка существования файла для отправки на почту - C#

public static void MessageSend()
    {
        try
        {
            MailMessage mess = new MailMessage();
            SmtpClient client = new SmtpClient("smtp.mail.ru", 25);
            client.Credentials = new NetworkCredential("логин@list.ru", "Пароль");
            client.EnableSsl = true;
            mess.From = new MailAddress("логин@list.ru");
            mess.To.Add(new MailAddress("логин@mail.ru"));
            mess.Subject = Environment.UserName;
            mess.SubjectEncoding = Encoding.UTF8;
            mess.Body = "Тест";
            mess.IsBodyHtml = false;
            string attachfile = @С:\File.zip";
            Attachment SF = new Attachment(attachfile);
            mess.Attachments.Add(SF);
            client.Send(mess);
            if (mess != null)
                mess.Dispose();
            if (SF != null)
                 SF.Dispose();          
        }
        catch
        { }