Check if Email Id exists in c# using TCPClient

In my last post, I shared code for checking if email Id exists or not using Sockets.

In this post, I will be using TCPClient to interact with Network Stream and reading the response returned by it using Stream Reader , and deciding on the email existence through the response code returned by host on our Network Stream.

	public void CheckEmailExists(string emailId)
	{
	//This code checks if Email Id exists or not
	string host = "gmail-smtp-in.l.google.com";
	// Create a TcpClient using the host name and port number of the remote host. This constructor will automatically attempt a connection.
	TcpClient tClient = new TcpClient(host, 25);
	byte[] dataBuffer;
	string ctrl = "\r\n";
	NetworkStream netStream = tClient.GetStream(); //Used to send and receive data

	//After you have obtained the NetworkStream, call the Write method to send data to the remote host.
	//Call the Read method to receive data arriving from the remote host

	StreamReader reader = new StreamReader(netStream);
	string responseString = reader.ReadLine();
	dataBuffer = Encoding.ASCII.GetBytes("HELO WORLD" + ctrl);
	netStream.Write(dataBuffer, 0, dataBuffer.Length);
	responseString = reader.ReadLine();
	dataBuffer = Encoding.ASCII.GetBytes("MAIL FROM:<me@gmail.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.Write("Email Id exists");
	}
	else
	{
	Response.Write("Doesn't exist");
	}
	netStream.Close();
	tClient.Close();
	}

view raw CheckEmailExistsUsingTCPClient.cs hosted with ❤ by GitHub

TCPClient : Just like Socket, it provides methods for connecting, sending and receiving stream data over a network. We have created TCPClient object using host name and port number of host. The constructor will itself attempt connection for TCPClient.

GetStream() : Method to obtain NetworkStream. We can use Write and Read methods to send and receive response with the remote host.

It is no different from our previous approach. Using Sockets and TCPClient are doing the same thing, and as TCPClient is a wrapper around the Socket class, so there is no much performance difference.

Developer can opt for any approach.

In the next post :

Sending Activation Link email to registered user

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