class Program
{
    static void Main(string[] args)
    {
        SendEmailBySmtp();
        SendEmailAsyncBySmtp();
    }

    static void SendEmailBySmtp()
    {
        MailMessage message = new MailMessage()
        {
            From = new MailAddress("test@example.com", "Test User"),
            Subject = "Subject",
            Body = "Body"
        };
        message.To.Add("test@example.com");
        message.CC.Add("test@example.com");
        message.BodyEncoding = UTF8Encoding.UTF8;
        message.DeliveryNotificationOptions = DeliveryNotificationOptions.OnFailure;
        using (SmtpClient client = new SmtpClient())
        {
            client.Port = 587;
            client.Host = "smtp.office365.com";
            client.EnableSsl = true;
            client.UseDefaultCredentials = false;
            client.Credentials = new System.Net.NetworkCredential("test@example.com", "password");
            client.Send(message);
        }
    }

    static async Task SendEmailAsyncBySmtp()
    {
        MailMessage message = new MailMessage()
        {
            From = new MailAddress("test@example.com", "Test User"),
            Subject = "Subject",
            Body = "Body"
        };
        message.To.Add("test@example.com");
        message.CC.Add("test@example.com");
        message.BodyEncoding = UTF8Encoding.UTF8;
        message.DeliveryNotificationOptions = DeliveryNotificationOptions.OnFailure;
        using (SmtpClient client = new SmtpClient())
        {
            client.Port = 587;
            client.Host = "smtp.office365.com";
            client.EnableSsl = true;
            client.UseDefaultCredentials = false;
            client.Credentials = new System.Net.NetworkCredential("test@example.com", "password");
            await client.SendMailAsync(message);
        }
    }
}

static void Main(string[] args)
    {
        SendEmailBySmtp();
        SendEmailAsyncBySmtp().RunAsync().GetAwaiter().GetResult();
    }