c# -以超文本标记语言发送电子邮件不起作用

using System;
using System.Net;
using System.Net.Mail;

class Program
{
    static void Main()
    {
        // 设置发件人和收件人信息
        string fromEmail = "your_email@example.com";
        string toEmail = "recipient_email@example.com";
        string subject = "Hello, World!";
        string body = "This is a test email.";

        // 创建MailMessage对象
        MailMessage message = new MailMessage(fromEmail, toEmail, subject, body);

        // 创建SmtpClient对象，并设置SMTP服务器信息
        SmtpClient smtpClient = new SmtpClient("smtp.example.com", 587);
        smtpClient.EnableSsl = true; // 启用SSL加密

        // 设置发件人的SMTP凭据
        smtpClient.Credentials = new NetworkCredential("your_username", "your_password");

        try
        {
            // 发送邮件
            smtpClient.Send(message);
            Console.WriteLine("Email sent successfully.");
        }
        catch (Exception ex)
        {
            Console.WriteLine("Failed to send email. Error message: " + ex.Message);
        }
    }
}