Can I check if an email address exists using .net?

问题:

Ive seen some php examples of how you can ping an inbox(without sending any mail to it) to check whether it exists. I was wondering if anyone knows if this is possible with .net? If it is Im going to write an app to do a bulk check on list of emails i have captured through my site.

回答1:

SMTP defines the VRFY command for this, but since abuse by spammers totally overwhelmed the number of legitimate uses, virtually every e-mail server in the world is configured to lie.

回答2:

No, it is impossible in principle to check if an email exists - independent of language. There is simply no protocol to do it.

There are some partial solutions, but none of them are reliable.

See How to check if an email address exists without sending an email? for details.

回答3:

What you mean about if you writing "check email"? Without sending some unique link for email owner you can't check this, you can only check syntax of email, and connection to smtp.

public static bool isEmail(string inputEmail)
{
   inputEmail  = NulltoString(inputEmail);
   string strRegex = @"^([a-zA-Z0-9_\-\.]+)@((\[[0-9]{1,3}" +
         @"\.[0-9]{1,3}\.[0-9]{1,3}\.)|(([a-zA-Z0-9\-]+\" + 
         @".)+))([a-zA-Z]{2,4}|[0-9]{1,3})(\]?)$";
   Regex re = new Regex(strRegex);
   if (re.IsMatch(inputEmail))
    return (true);
   else
    return (false);
}

smtp check

string[] host = (address.Split('@'));
string hostname = host[1];

IPHostEntry IPhst = Dns.Resolve(hostname);
IPEndPoint endPt = new IPEndPoint(IPhst.AddressList[0], 25);
Socket s= new Socket(endPt.AddressFamily, 
        SocketType.Stream,ProtocolType.Tcp);
s.Connect(endPt);

回答4:

http://www.codicode.com/art/free_asp_net_email_validator_verifier.aspx. Use the dll reference to your code. It is free both for personal use and redistribution. It checks for the domain name existence without actually sending an email.

回答5:

This is not foolproof. The best you can do is check syntax and see if the domain name resolves.

Email syntax RegEx: (?<username>#?[_a-zA-Z0-9-+]+(\.[_a-zA-Z0-9-+]+)*)@(?<domain>[a-zA-Z0-9-]+(\.[a-zA-Z0-9-]+)*\.(([0-9]{1,3})|([a-zA-Z]{2,3})|(aero|arpa|asia|coop|info|jobs|mobi|museum|name|travel)))

回答6:

protected bool checkDNS(string host, string recType = "MX")
{
    bool result = false;
    try
    {
        using (Process proc = new Process())
        {
            proc.StartInfo.FileName = "nslookup";
            proc.StartInfo.Arguments = string.Format("-type={0} {1}", recType, host);
            proc.StartInfo.CreateNoWindow = true;
            proc.StartInfo.ErrorDialog = false;
            proc.StartInfo.RedirectStandardError = true;
            proc.StartInfo.RedirectStandardOutput = true;
            proc.StartInfo.UseShellExecute = false;
            proc.StartInfo.WindowStyle = ProcessWindowStyle.Hidden;
            proc.OutputDataReceived += (object sender, DataReceivedEventArgs e) =>
                {
                    if ((e.Data != null) && (!result))
                        result = e.Data.StartsWith(host);
                };
            proc.ErrorDataReceived += (object sender, DataReceivedEventArgs e) =>
                {
                    if (e.Data != null)
                    {
                        //read error output here, not sure what for?
                    }
                };
            proc.Start();
            proc.BeginErrorReadLine();
            proc.BeginOutputReadLine();
            proc.WaitForExit(30000); //timeout after 30 seconds.
        }
    }
    catch
    {
        result = false;
    }
    return result;
}