public string smtpService = "smtp.qq.com";//发送邮箱的smtp服务地址
public string sendEmail = "xxxx@qq.com";//发送邮箱的账号
public string sendpwd = "xxxxx";//发送邮箱的密码
public string userPassword = "oelovozltpffbacf";//发送邮箱的授权码

public string Email()
{
    try
    {
        string Mai = "xxxx@qq.com,xxxx@qq.com";//接收人邮箱(这里定义了多个循环发送，也可以定义一个去掉循环)

        string[] address = Mai.Split(‘,‘);
        for (int i = 0; i < address.Length; i++)
        {
            SmtpClient smtpClient = new SmtpClient();
            smtpClient.EnableSsl = true;
            smtpClient.UseDefaultCredentials = false;
            smtpClient.DeliveryMethod = SmtpDeliveryMethod.Network;//指定电子邮件发送方式
            smtpClient.Host = smtpService; //指定SMTP服务器
            smtpClient.Credentials = new System.Net.NetworkCredential(sendEmail, userPassword);//用户名和授权码
            // 发送邮件设置
            MailMessage mailMessage = new MailMessage(sendEmail, address[i]); // 发送人和收件人
            mailMessage.Subject = "";//邮件主题
            mailMessage.Body = "";//邮件内容
            mailMessage.BodyEncoding = Encoding.UTF8;//正文编码
            mailMessage.IsBodyHtml = true;//设置为HTML格式
            mailMessage.Priority = MailPriority.Low;//优先级
            smtpClient.Send(mailMessage);
        }
        return "发送成功";
    }  
    catch (Exception)
    {
        return "邮件发送异常";
    }
}