VB.NET

Verify DKIM-Signature Headers in Downloaded Email

See more DKIM / DomainKey Examples

Downloads email from an IMAP server and verifies the DKIM-Signature header(s) in each email, if present. VB.NET

Dim success As Boolean = False

' This example requires the Chilkat API to have been previously unlocked.
' See Global Unlock Sample for sample code.

Dim imap As New Chilkat.Imap

' Connect to an IMAP server, login, select mailbox..
' Use TLS 
imap.Ssl = True
imap.Port = 993
success = imap.Connect("imap.example.com")
If (success = True) Then
    success = imap.Login("myLogin","myPassword")
    If (success = True) Then
        success = imap.SelectMailbox("Inbox")
    End If

End If

If (success <> True) Then
    Debug.WriteLine(imap.LastErrorText)
    Exit Sub
End If


Dim dkim As New Chilkat.Dkim

' Download a max of 10 emails and verify any DKIM-Signature headers
' that are present.

' Download emails by sequence numbers (not UIDs).
Dim bUid As Boolean = False
Dim seqNum As Integer
Dim j As Integer
Dim n As Integer = imap.NumMessages
If (n > 10) Then
    n = 10
End If


Dim json As New Chilkat.JsonObject
json.EmitCompact = False

' To verify DKIM-Signature headers, we need the exact unmodified MIME bytes of each email.
Dim mimeData As New Chilkat.BinData
seqNum = 1
While seqNum <= n
    ' The FetchSingleBd method was introduced in v9.5.0.76
    success = imap.FetchSingleBd(seqNum,bUid,mimeData)
    If (success <> True) Then
        Debug.WriteLine(imap.LastErrorText)
        Exit Sub
    End If


    ' Get the number of DKIM-Signature headers.
    Dim numDkim As Integer = dkim.NumDkimSigs(mimeData)

    ' Verify each..
    j = 0
    While j < numDkim
        Debug.WriteLine("------ DKIM Signature " & j)

        success = dkim.DkimVerify(j,mimeData)
        If (success <> True) Then
            Debug.WriteLine("Not valid.")
        Else
            Debug.WriteLine("valid.")
        End If


        ' Show the additional information about the signature verification
        json.Load(dkim.VerifyInfo)
        Debug.WriteLine(json.Emit())

        ' The JSON contains information such as this:

        ' 	{
        ' 	  "domain": "amazonses.com",
        ' 	  "selector": "7v7vs6w47njt4pimodk5mmttbegzsi6n",
        ' 	  "publicKey": "MIGfMA0GCSqG...v2GvWPqGHz6uqeQIDAQAB",
        ' 	  "canonicalization": "relaxed/simple",
        ' 	  "algorithm": "rsa-sha256",
        ' 	  "signedHeaders": "Subject:From:To:Date:Mime-Version:Content-Type:References:Message-Id:Feedback-ID",
        ' 	  "verified": "yes"
        ' 	}

        j = j + 1
    End While
    seqNum = seqNum + 1
End While

success = imap.Disconnect()