检测 邮箱地址 是否存在[C#]

[检测某个邮箱地址是否存在]

public  class CheckEmail
{
    private static string mailQQ = "http://emailreg.qq.com/cgi-bin/signup/ajaxcheckmail?type=1&email={0}";
    private static string mailFox = "http://emailreg.qq.com/cgi-bin/signup/ajaxcheckmail?type=3&email={0}"; 
    private static string mail163 = "http://reg.email.163.com/mailregAll/checkuname.do?uname={0}g&random={1}";
    public static bool IsExist(string email)
    {
        return NoExist(email) ? false : true;
    }
    public static bool NoExist(string email)
    {
        if (email.IndexOf("@") > 0)
        {
            string end = email.Substring(email.IndexOf("@") + 1);
            switch (end)
            {
                case "qq.com": return CheckMailQQ(email);
                case "foxmail.com": return CheckMailFox(email);
                case "163.com": return CheckMail163(email, EnumMail163.mail163) || CheckMail163(email, EnumMail163.vip163);
                case "126.com": return CheckMail163(email, EnumMail163.mail126) || CheckMail163(email, EnumMail163.vip126);
                case "yeah.net": return CheckMail163(email, EnumMail163.mailyeah);                     
            }
        }
        return false;
    }
    
//wang@qq.com
public static bool CheckMailQQ(string email)
    {
        string url = string.Format(mailQQ, email);
        var doc = GetXmlData(url);
        if (doc.Descendants("result").FirstOrDefault() != null)
        {
            return doc.Descendants("result").FirstOrDefault().Value.Trim()== "0";
        }
        return false;

    }
    //dfasdfds@foxmail.com
    public static bool CheckMailFox(string email)
    {
        string url = string.Format(mailFox, email);
        var doc = GetXmlData(url);
        if (doc.Descendants("result").FirstOrDefault() != null)
        {
            return doc.Descendants("result").FirstOrDefault().Value.Trim() == "0";
        }
        return false;

    }
private static bool CheckMail163(string email, EnumMail163 type)
    {
        Random rnd = new Random();
        string name = email.Substring(0, email.LastIndexOf("@"));
        string url = string.Format(mail163, name,(rnd.Next()*0.00000001).ToString());
        var dic = GetKeyValueData(url);
        if (dic.ContainsKey(type.ToString()))
            return bool.Parse(dic[type.ToString()]);             
        return false;

    }
    private static IDictionary<string, string>  GetKeyValueData(string requestUrl)
    {
        IDictionary<string, string> valueDic = new Dictionary<string, string>();
        valueDic.Clear();
        var request = HttpWebRequest.Create(requestUrl) as HttpWebRequest;
        var response = request.GetResponse() as HttpWebResponse;
        using (var sr = new StreamReader(response.GetResponseStream()))
        {
        var result=sr.ReadToEnd();
        var valueArray = result.Split(new char[] { ',',':'});
        for (int i = 0; i < valueArray.Length;i+= 2)
            valueDic.Add(valueArray[i], valueArray[i + 1]);                  
        }
        return valueDic;
    }
private static XDocument GetXmlData(string requestUrl)
{
    XDocument doc = null;
    var request = HttpWebRequest.Create(requestUrl) as HttpWebRequest;
    var response = request.GetResponse() as HttpWebResponse;
    using (var sr = new StreamReader(response.GetResponseStream()))
    {
        doc = XDocument.Parse(sr.ReadToEnd());
    }
    return doc;
}
}

public enum EnumMail163
{   mail163,
    mail126,
    mailyeah,
    vip163,
    vip126,
    vip188
}