Check Domain Name Exist or not using C# and VB.Net in ASP.Net

Hi khdirfan,

You can perform a DNS lookup on the domain name or Ip Address.

For more information refer below link.

http://msdn.microsoft.com/en-us/library/ms143998.aspx

Check this example. Now please take its reference and correct your code.

HTML

<asp:TextBox runat="server" ID="txtEmail" />
<asp:Button Text="Validate Domain" runat="server" OnClick="ValidateDomain" />

Code

C#

protected void ValidateDomain(object sender, EventArgs e)
{
    System.Net.Mail.MailAddress mailAddress = new System.Net.Mail.MailAddress(txtEmail.Text.Trim());
    string domainName = mailAddress.Host;
    ClientScript.RegisterClientScriptBlock(this.GetType(), "", "alert('" + IsValidateDomainName(domainName) + "')", true);
}

public bool IsValidateDomainName(string domainName)
{
    bool isDomainExist = false;
    System.Net.IPHostEntry host;
    try
    {
        host = System.Net.Dns.GetHostEntry(domainName);
        if (host != null)
        {
            isDomainExist = true;
        }
    }
    catch (Exception ex)
    {
        if (ex.Message == "No such host is known")
        {
            isDomainExist = false;
        }
    }

    return isDomainExist;
}

VB.Net

Protected Sub ValidateDomain(ByVal sender As Object, ByVal e As EventArgs)
    Dim mailAddress As Net.Mail.MailAddress = New Net.Mail.MailAddress(txtEmail.Text.Trim())
    Dim domainName As String = mailAddress.Host
    ClientScript.RegisterClientScriptBlock(Me.GetType(), "", "alert('" & IsValidateDomainName(domainName) & "')", True)
End Sub

Public Function IsValidateDomainName(ByVal domainName As String) As Boolean
    Dim isDomainExist As Boolean = False
    Dim host As Net.IPHostEntry
    Try
        host = Net.Dns.GetHostEntry(domainName)
        If host IsNot Nothing Then
            isDomainExist = True
        End If
    Catch ex As Exception
        If ex.Message = "No such host is known" Then
            isDomainExist = False
        End If
    End Try

    Return isDomainExist
End Function

Screenshots

Valid

In valid