In this article, How we can verify if email address exists or not using C#, you can use this c# validate email address code while registering the user on your Web or Desktop application, to check if the email id entered by user really exists or not. So you will get two answers in this article, how to validate email address in c# and how to verify email address exists or not using C#.

We can divide this verification process into two part:

  1. Validate the email address format
  2. Verify email address exists or not using third party API

C# email validation (regex expression used)

Let's begin with checking if an email address is valid using regex validation in C#

using System;
using System.Text.RegularExpressions;
					
public class Program
{
	public static void Main()
	{ 
		var stringToTest="email@gmail.com";
		var stringtoTest2= "NotAValid@h.com";
	    string pattern = null;
	    pattern = "^([0-9a-zA-Z]([-\\.\\w]*[0-9a-zA-Z])*@([0-9a-zA-Z][-\\w]*[0-9a-zA-Z]\\.)+[a-zA-Z]{2,9})$";
		
		
		//check first string
	   if (Regex.IsMatch(stringToTest , pattern))
	   {		  
		    Console.WriteLine(stringToTest+ " is Valid Email address ");
	   }
	   else
	   {
		    Console.WriteLine(stringToTest + " is Not a Valid Email address");			
	   }

		//check second string
	   if (Regex.IsMatch(stringtoTest2 , pattern))
	   {		  
		    Console.WriteLine(stringtoTest2+ " is Valid Email address ");
	   }
	   else
	   {
		    Console.WriteLine(stringtoTest2 + " is Not a Valid Email address");			
	   }
	}
}

Output:

email@gmail.com is Valid Email address 
NotAValid@h.com is Not a Valid Email address

Here is the dotnet fiddle link https://dotnetfiddle.net/kDVo4v

Email address validation in asp.net using RegularExpressionValidator

We are still validating email address not verifying it yet, so to do that using RegularExpressionValidator in ASP.NET Forms, we can use the below C# and .aspx code

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="EmailIdValidate.Default" %>

<!DOCTYPE html>
<script runat="server">
    protected void Button1_Click(object sender, EventArgs e)
    {
        Label1.Text = "Your email: " + TextBox1.Text.ToString();
    }
</script>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Validate email address using RegularExpressionValidator in ASP.NET</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <h2 style="color:Red">RegularExpressionValidator: email</h2>
        <asp:Label 
             ID="Label1" 
             runat="server"
             Font-Bold="true"
             Font-Italic="true"
             Font-Size="Large"
             ForeColor="SeaGreen"
             >
        </asp:Label>

        <br /><br />
        <asp:Label ID="Label2" runat="server" Text="Email">
        </asp:Label>
        <asp:TextBox  ID="TextBox1" runat="server" >
        </asp:TextBox>

        <asp:RequiredFieldValidator 
             ID="RequiredFieldValidator1"
             runat="server"
             ControlToValidate="TextBox1"
             Text="*"
             >
        </asp:RequiredFieldValidator>

        <asp:RegularExpressionValidator 
            ID="RegularExpressionValidator1"
            runat="server" 
             ValidationExpression="\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*"
            ControlToValidate="TextBox1"
            ErrorMessage="Input valid email address!"
            >
        </asp:RegularExpressionValidator>

        <br /><br />
        <asp:Button 
             ID="Button1" 
             runat="server" 
             Text="Submit email"
             Font-Bold="true"
             ForeColor="DodgerBlue" 
             OnClick="Button1_Click"
             />
    </div>
    </form>
</body>
</html>

Output:

email-address-validation-in-asp-net-min.gif

Note: You may need to add key <add key="ValidationSettings:UnobtrusiveValidationMode" value="None" /> in Web.Config under configuration->appsettings to avoid error.

Verify email address exists or not using C#

Now, we have found the C# way to validate it, but validation only checks the pattern of the email id, it doesn't provide us perfect result if that user's really exists or not.

So to verify if email address really exists or not, we will be using a API. In this example, we will use https://quickemailverification.com api, which helps us to verify100 emails daily for free, so you can sign up for it and get your free API key.

c-sharp-verify-email-address-exists-min.png

Once you sign up on QuickEmailVerification website, you can to "apisettings" in the menu after login and get your api key as shown below

api-key-for-c-sharp-verify-email-address-exists-min.png

This key will help us in verifying the email-address.

So, for testing purposes, I will be creating a Console App in my Visual Studio, navigate to "File"->"New"->"Project"-> Select the "Console application" , name it, and click "Ok"

In your Program.cs, use the below C# code and replace the "API_Key" with your valid api key and provide the email address to verify

using System;
using System.Net;
using System.IO;

namespace EmailVerifyConsole
{
    class Program
    {
        static void Main(string[] args)
        {
            try
            {
                string apiKey = "API_key";
                string emailToValidate = "YourEmailToVerify@example.com";
                string responseString = "";
                string apiURL = "http://api.quickemailverification.com/v1/verify?email=" + WebUtility.UrlEncode(emailToValidate) + "&apikey=" + apiKey;

                HttpWebRequest request = (HttpWebRequest)WebRequest.Create(apiURL);
                request.Method = "GET";

                using (WebResponse response = request.GetResponse())
                {

                    using (StreamReader ostream = new StreamReader(response.GetResponseStream()))
                    {
                        responseString = ostream.ReadLine();
                    }
                }
                Console.WriteLine(responseString);
                Console.ReadKey();
            }
            catch (Exception ex)
            {
                //Catch Exception - All errors will be shown here - if there are issues with the API
            }
        }
    }
}

Once your build and execute the application, you will get JSON response as below, if email id is valid

{
  "result": "valid",
  "reason": "accepted_email",
  "disposable": "false",
  "accept_all": "false",
  "role": "false",
  "free": "true",
  "email": "YourEmailAddress@gmail.com",
  "user": "YourEmailAddress",
  "domain": "gmail.com",
  "mx_record": "gmail-smtp-in.l.google.com",
  "mx_domain": "google.com",
  "safe_to_send": "true",
  "did_you_mean": "",
  "success": "true",
  "message": ""
}

otherwise (if email is not valid , example : hasdsad@gmail.uk.com) you will get output as below

{
  "result": "invalid",
  "reason": "rejected_email",
  "disposable": "false",
  "accept_all": "false",
  "role": "false",
  "free": "false",
  "email": "hasdsad@gmail.uk.com",
  "user": "hasdsad",
  "domain": "gmail.uk.com",
  "mx_record": "mx0.123-reg.co.uk",
  "mx_domain": "123-reg.co.uk",
  "safe_to_send": "false",
  "did_you_mean": "hasdsad@gmail.com",
  "success": "true",
  "message": ""
}

In real-world application, you would have to first validate the email-address then verify it, before saving it into your database, as only valid and verified email-address is useful for us.

You can combine both the C# code to validate and verify the email-address, here is the example of it.

using System;
using System.Net;
using System.IO;
using System.Text.RegularExpressions;

namespace EmailVerifyConsole
{
    class Program
    {
        static void Main(string[] args)
        {
            try
            {
                //email to validate and then verify
                var EmailToValidateVerify = "email@gmail.com";
                
                string pattern = null;
                pattern = "^([0-9a-zA-Z]([-\\.\\w]*[0-9a-zA-Z])*@([0-9a-zA-Z][-\\w]*[0-9a-zA-Z]\\.)+[a-zA-Z]{2,9})$";

                //Validate email first 
                if (Regex.IsMatch(EmailToValidateVerify, pattern))
                {
                    Console.WriteLine(EmailToValidateVerify + " is Valid Email address ");
                    //email validated call API function to verify it now
                    VerifyEmail(EmailToValidateVerify);
                }
                else
                {
                    Console.WriteLine(EmailToValidateVerify + " is Not a Valid Email address");
                }
                
            }
            catch (Exception ex)
            {
                //Catch Exception - All errors will be shown here - if there are issues with the API
            }
        }

        public static void VerifyEmail(string emailToValidate)
        {
            //your API key from quick email verification site
            string apiKey = "API_Key";           

            string responseString = "";
            string apiURL = "http://api.quickemailverification.com/v1/verify?email=" + WebUtility.UrlEncode(emailToValidate) + "&apikey=" + apiKey;

            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(apiURL);
            request.Method = "GET";

            using (WebResponse response = request.GetResponse())
            {

                using (StreamReader ostream = new StreamReader(response.GetResponseStream()))
                {
                    responseString = ostream.ReadLine();
                }
            }
            Console.WriteLine(responseString);
            Console.ReadKey();
        }
    }
}

So, in this way we can validate and then verify email address using C# code.