Validate email address

Hi Michael,

You can confirm the domain name by doing a Whois search. There's some code here
for doing that.

 http://www.**--****.com/ 

 http://www.**--****.com/ 

Ken





I have a web form that collects the users email address.

How can I validate the email address, at the very least confirm that the
domain exists?

Thanks

-- 
Michael Tissington
Oaklodge Technologies
 http://www.**--****.com/ 

This is what I use. I don't know if it is foolproof or not but I haven't had
any problems with it.
in my aspx page
<asp:textbox id="Email1" size="40" runat="server"/>

                       <asp:RegularExpressionValidator id="RequiredEmail1"
runat="server"
                  ControlToValidate="Email1"
                            InitialValue=""

ValidationExpression="[a-zA-Z_0-9.]+@[a-zA-Z_0-9.]+\.(com|net|org|edu|mil)$"
                  Display="Static"
                  Font-Name="verdana" Font-Size="10pt">
                     * valid e-mail address required
          </asp:RegularExpressionValidator>
                        <asp:CustomValidator id="CustomValidator1"
runat="server"
              ControlToValidate="Email1"
           OnServerValidate="ServerValidate"
                            Display="Static"
                            Font-Name="verdana" Font-Size="10pt">
                             * valid mail server name required.
                        </asp:CustomValidator>


 in my codebehind page.

Sub ServerValidate (sender As Object, dnsvalue As ServerValidateEventArgs)
            dim strDomain as string
            dnsvalue.IsValid = False
            Try
                dim int as integer
                int = instr(2,dnsvalue.Value,"@")
                strDomain = mid(dnsvalue.value,int+1,999)
                If not Dns.GetHostByName(strDomain).hostname is null Then
                    dnsvalue.IsValid = True
                End If
            Catch
            End Try
            RequiredEmail1.text = ""

 End Sub

Thanks for the suggestion. I'm still trying to figure the syntax but it
seems to work great. I find these expression a bit of a challenge!




@"^([\w-\.]+)@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.)|(([\w-]+\.)+))([a-zA

Let see if I got this right.
^([\w-\.]+)@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.)|(([\w-]+\.)+))([a-zA-Z
]{2,4}|[0-9]{1,3})(\]?)$
is

^  is start with
[w-\.] is basically anything
then @
then either
First side
1) 3- 1 to 3 digit numbers separated by a . plus . (I guess this is for
using an ip address) or

2) \w is any word or words plus .
plus
second side
either
1) 2-4 letters or

2) 1-3 numbers
the $ is the end

The parts I don't understand are
why is there a - after the each w and why the two w's are different (seem
like the second w should be the same as the first set.
what does the (\]?) mean.








@"^([\w-\.]+)@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.)|(([\w-]+\.)+))([a-zA



the

It breaks down like this:

([\w-\.]+) : One or more words separated by hyphens or full stops
@ : The '@' symbol (never... ;)
(\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.) : The first three segments of a
dotted ip address preceded by a '['
(([\w-]+\.)+)) : At least one subdomain (word) followed by a full stop
[a-zA-Z]{2,4} : Two to four characters in the range a - z (case insensitive)
[0-9]{1,3})(\]?) : The last portion of a dotted ip address followed by an
optional ']' character

I have to admit that it seems a bit odd that the final ']' is optional and
not required. I'd have to check the RFC on email addresses to check that
one.

Personally, I would have rewritten it as:

^([\w-\.]+)@(\[(\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.){3}[0-9]{1,3}\])|((([
\w-]+\.)+))[a-zA-Z]{2,4})$

Bear in mind this might not work - I've not had a chance to test it yet!






^([\w-\.]+)@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.)|(([\w-]+\.)+))([a-zA-Z






@"^([\w-\.]+)@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.)|(([\w-]+\.)+))([a-zA

Here is a web which collects all helpful information on this issue 
(including Whois, regular expression...), you may take a look at it:

 http://www.**--****.com/ 

Luke

"Microsoft Security Announcement: Have you installed the patch for 
Microsoft Security Bulletin MS03-026?? If not Microsoft strongly advises 
you to review the information at the following link regarding Microsoft 
Security Bulletin MS03-026 
 http://www.**--****.com/ 
visit Windows Update at  http://www.**--****.com/  to install the 
patch.  Running the SCAN program from the Windows Update site will help to 
insure you are current with all security patches, not just MS03-026."