邮件群发怎么做（asp.net）

/// <summary>
/// 发送简单邮件--从配置文件获取基本配置
/// </summary>
/// <param name="towebmail">接收人外部邮件地址</param>
/// <param name="subject">标题</param>
/// <param name="content">内容</param>
/// <param name="isbodyhtml">是否启用html方式发送</param>
/// <returns>成功则返回true，失败则返false</returns>
public bool SendSimpleMail(string towebmail, string subject, string content,bool isbodyhtml)
{
try
{
//实例化邮件发送对象并赋值（传参）
MailMessage mailmessage = new MailMessage();
MailAddress mailaddress = new MailAddress(this.Address);

mailmessage.From = mailaddress;
mailmessage.IsBodyHtml = isbodyhtml;
if (towebmail != "")