How to check if Email id exists in c#

How to Check if Email Id exists or Not

You can validate email id input by your user in application.
Email can be validated using :
1) Socket
2) TcpClient
Both comes with System.Net.Sockets namespace

Here' the code and the explanation :

	public void EmailExistsOrNot(string emailId)
	{
	//This code checks if Email Id exists or not
	string host = "gmail-smtp-in.l.google.com";
	byte[] dataBuffer;
	string ctrl = "\r\n";
	Socket s = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
	IPAddress[] IPs = Dns.GetHostAddresses(host);
	s.Connect(IPs[0], 25);
	NetworkStream netStream = new NetworkStream(s);
	StreamReader reader = new StreamReader(netStream);
	string responseString = reader.ReadLine();
	//HELO : The client sends this command to the SMTP server to identify itself and initiate the SMTP conversation.
	//The domain name is usually sent as an arguement together with command
	dataBuffer = Encoding.ASCII.GetBytes("HELO client.demo.com" + ctrl);
	//Call the Write method to send data to the remote host.
	netStream.Write(dataBuffer, 0, dataBuffer.Length);
	//Call the Read method to receive data arriving from the remote host
	// The server acknowledges to HELO command and is ready for the service
	responseString = reader.ReadLine();
	dataBuffer = Encoding.ASCII.GetBytes("MAIL FROM:<customercare@hotehomes.com>"+ctrl);
	netStream.Write(dataBuffer, 0, dataBuffer.Length);
	responseString = reader.ReadLine();
	dataBuffer = Encoding.ASCII.GetBytes("RCPT TO:<" + emailId + ">" + ctrl);
	netStream.Write(dataBuffer, 0, dataBuffer.Length);
	responseString = reader.ReadLine();
	if(responseString.Contains("250"))
	{
	Response.WriteLine("EmailId exists");
	}
	else
	{
	Response.WriteLine("EmailId doesn't exist");
	}
	}

view raw EmailExists.cs hosted with ❤ by GitHub

• Socket provides properties and methods for network communication, allowing both synchronous and asynchronous data transfer. More about Sockets : Sockets

• IPAddress[] IPs = Dns.GetHostAddresses(host);

         Gets the I.P address of your host which you are trying to connect with.
         Connecting the socket with port number is very important otherwise it will throw exception.
         More about Socket.Connect : Socket.Connect()

• NetworkStream : Provides methods for sending and receiving data over Stream sockets. To create instance of NetworkStream, we must provide a connected socket. Once  the network stream is instantiated, we use Write() method to send data to remote host and StreamReader use Read method to receive data arriving from remote host on NetworkStream.

dataBuffer = Encoding.ASCII.GetBytes("RCPT TO:<" + emailId + ">" + ctrl);

Here, we pass the email Id which is to be checked. If the ID exists , the remote host returns with 250 code, and if it doesn't , returns 550.

This is how we can check If email Id exists or not.
Note : Your ISP might have block Port 25 to refrain spammers . In that case RCPT to command will return 550 even if EmailId exists.

That is why during registration, most websites send an Activation Link mail which helps them recognize that the email Id is valid. 

In next posts  :

1) Check if Email Id exists using TcpClient

2) How to send Activation Link mail from your application