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Validating Email Address Against The Mail Server

Web Bureau

18 November 2011 by Web Bureau

I'm sure you have all came across the problem of automatic spamming of forms using a robot.

One solution to this is to validate the email address on the form by checking that it is a valid domain name and chacking to see if the Mail Server exists.


  • The code below extracts the domain name from the email address entered
  • Carrys out a name server lookup
  • If found you know that the email address is from a valid domain.


Dim address As String = ""
Dim host As String() = (address.Split("@"c))
Dim hostname As String = host(1)
Dim info As New ProcessStartInfo()
Dim ns As Process
Dim sout As StreamReader
Dim mailserver As String = ""
Dim response As String = ""

info.UseShellExecute = False
info.RedirectStandardInput = True
info.RedirectStandardOutput = True
info.FileName = "nslookup"
info.Arguments = "-type=MX " + sDomain.ToUpper.Trim
ns = Process.Start(info)

sout = ns.StandardOutput
Dim reg As Regex = New Regex("mail exchanger = (?<server>[^\\\s]+)")

Do While (sout.Peek() > -1)
response = sout.ReadLine()
Dim amatch As Match = reg.Match(response)
If (amatch.Success) Then
mailserver = amatch.Groups("server").Value
Exit Do
End If

Return mailserver

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