Some times website owners need to allow users to get registered on their website or subscribe to newsletters on their website, by allowing users to provide their email addresses. But how would you verify that the user provided email addresses are genuine and valid, to avoid bounced email messages.
This article will demonstrate how to verify that the email address provided by a user is a valid email address, using a sample code.
ASP.NET Provides Built-in DNS Resolving Support. DNS class from System.Net namespace can be used to resolve DNS hostnames into IP addresses. Using this class we could verify email addresses and ensure that the domain name specified by the user actually resolved to an existing domain name.
Following is the sample code that uses the DNS classes and its Resolve method, along with a regular expression, to build a fairly reliable email address validation technique in ASP.NET.
<%@ Import Namespace=”System.Net” %>
<%@ Import Namespace=”System.Net.Sockets” %>
<%@ Import Namespace=”System.Text.RegularExpressions” %>
<script language=”VB” runat=”server”>
Sub btnSubmit_OnClick(ByVal source As Object, ByVal e As EventArgs)
'Check to make sure that the email addy is in the right form
Dim strEmail As String, strPattern As String
strEmail = txtEmail.Text
strPattern = "^[\w-_\.]+\@([\w]+\.)+\w+$"
If Not Regex.IsMatch(strEmail, strPattern, "i") Then
'Invalid email address form!
Response.Write("<font color=red><i>Your email address is in an" & _
" illegal format.</i></font><p>")
'Check to see if the domain name entered in the email address exists
Dim strDomain As String
strDomain = strEmail.Substring(strEmail.IndexOf("@") + 1)
'Attempt to Resolve the hostname
Dim strIP As String
strIP = DNS.Resolve(strDomain).ToString()
'If we reach here, we have a valid email address, so do whatever
'processing or whatnot needs to be done...
Response.Write("<b>Valid email address. Your domain name has " & _
"an IP of " & strIP & ". Thank you!</b>")
Catch se As SocketException
'The DNS resolve was unsuccessful...
strIP = se.Message
Response.Write("<font color=red><i>" & strIP & "</i></font><p>")
<b>Enter your Email address:</b>
<asp:textbox id=”txtEmail” runat=”server” />
<asp:button id=”btnSubmit” runat=”server” Text=”Check Email” OnClick=”btnSubmit_OnClick” />
Additionally, I would recommend that you force user to respond to a confirmation email message sent to his provided email address, to guarantee that the user has provided a valid email address.