"Pinging" an email address using VB.Net coding - vb.net

Question

Is there a way in VB.Net to "Ping" an email address to see if that email is a real one that does not give any errors?
If yes, can you show what the VB.Net coding looks like to implement this?
I plan to use this in an app that requires the Customer email and it would be nice to validate it as the call taker enters it into a form before saving the Customer details.
Here is the code we are using to send an email promotion to all of the customers in our customer table:
Private Sub RibbonButtonSendTestEmail_Click(sender As System.Object, e As System.EventArgs) Handles RibbonButtonSendTestEmail.Click
Dim SmtpServer As New SmtpClient()
Dim mail As New MailMessage()
Dim strSqlStatement As String = "Select CustomerName, Email " & _
"From Customers "
Using objSqlCommand As SqlCommand = New SqlCommand(strSqlStatement, ObjConnection)
With objSqlCommand
' Open the SqlConnection before executing the query.
'---------------------------------------------------
Cursor = Cursors.WaitCursor
ObjConnection.Open()
Dim objDataReader As SqlDataReader = .ExecuteReader()
' Go through all the customers and send out the promotion emails.
'----------------------------------------------------------------
If objDataReader.HasRows Then
SmtpServer.Host = TextBoxSMTPServer.Text
SmtpServer.Port = TextBoxPort.Text
If TextBoxUseSSL.Text = "Yes" Then
SmtpServer.EnableSsl = True
Else
SmtpServer.EnableSsl = False
End If
If TextBoxUseDefaultCredentials.Text = "Yes" Then
SmtpServer.UseDefaultCredentials = True
Else
SmtpServer.UseDefaultCredentials = False
End If
SmtpServer.Credentials = New Net.NetworkCredential(TextBoxUserName.Text, TextBoxPassword.Text)
While objDataReader.Read()
Try
mail.To.Add(objDataReader("Email").ToString)
mail.From = New MailAddress(TextBoxEmailFrom.Text)
mail.Subject = "Promotion: " & TextBoxID.Text
mail.Body = "Dear " & objDataReader("CustomerName") & "," & vbCrLf & vbCrLf & TextBoxPromotionBodyText.Text
SmtpServer.Send(mail)
Catch exSMTP As SmtpException
MessageBox.Show("Sorry, I could not send an email for: " & _
vbCrLf & objDataReader("CustomerName") & "." & vbCrLf & _
"Please make sure it is correct.", _
"Error")
Catch exFormat As FormatException
MessageBox.Show("Sorry, this customer's email is not properly formatted: " & _
vbCrLf & objDataReader("CustomerName") & "." & vbCrLf & _
"Please make sure it is correct.", _
"Error")
End Try
End While
LabelEmail.Text = "Sent email promotions to the customers."
End If
objDataReader.Close()
ObjConnection.Close()
Cursor = Cursors.Default
End With ' objSqlCommand
End Using ' objSqlCommand
End Sub

Answer 1

Yes it's perfectly possible:
1 DNS Lookup the MX records for the domain
There may be multiples, you can pick anyone, although technically the one with the lowest preference indicator is the prefered one.
2 TCP Connect to the mail server (port 25)
Say hello: HELO
Identify yourself: mail from:<test#example.com>
Say who you're writing to: rcpt to<testaddress#example.com>
At this point the server will reply with a response, you'll get an OK or a 550 error with a message (like: The email account that you tried to reach does not exist)
Disconnect and the message will be dropped.
But dude, you want the VB code to do this? You just need a DNS talking piece and TCP connection building piece (or likely there are some SMTP libraries out there that'll do all this for you - or provide you with inspiration to figure it out yourself). Don't forget you can probably find a C# code example that does it and use Visual Studio's conversion tool to switch it to VB.
Note
Many domains have black holes/catch alls... the former will accept any email address and just delete it if it's invalid, the latter will accept any email address and forward them to a central account (no guarantees as to what happens then... sell the sender's address to spammers?) In both cases you won't get the 550 message, so you can never be certain.

Answer 2

There most reliable way to do this is to send a test email and have the recipient verify receipt by clicking on a link, which you then read and mark the email as active.
You should do primitive checks on the syntax of the email using regular expressions, but beyond that the most reliable way to validate an email is to attempt delivery and confirm the receipt.