(Visual FoxPro) Verify DKIM-Signature Headers in Downloaded Email

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

Chilkat ActiveX Downloads ActiveX for 32-bit and 64-bit Windows

LOCAL loImap
LOCAL lnSuccess
LOCAL loDkim
LOCAL lnBUid
LOCAL lnSeqNum
LOCAL j
LOCAL n
LOCAL loJson
LOCAL loMimeData
LOCAL lnNumDkim

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

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.Imap')
loImap = CreateObject('Chilkat.Imap')

* Connect to an IMAP server, login, select mailbox..
* Use TLS 
loImap.Ssl = 1
loImap.Port = 993
lnSuccess = loImap.Connect("imap.someMailServer.com")
IF (lnSuccess = 1) THEN
    lnSuccess = loImap.Login("myLogin","myPassword")
    IF (lnSuccess = 1) THEN
        lnSuccess = loImap.SelectMailbox("Inbox")
    ENDIF

ENDIF

IF (lnSuccess <> 1) THEN
    ? loImap.LastErrorText
    RELEASE loImap
    CANCEL
ENDIF

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.Dkim')
loDkim = CreateObject('Chilkat.Dkim')

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

* Download emails by sequence numbers (not UIDs).
lnBUid = 0

n = loImap.NumMessages
IF (n > 10) THEN
    n = 10
ENDIF

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.JsonObject')
loJson = CreateObject('Chilkat.JsonObject')
loJson.EmitCompact = 0

* To verify DKIM-Signature headers, we need the exact unmodified MIME bytes of each email.
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.BinData')
loMimeData = CreateObject('Chilkat.BinData')
lnSeqNum = 1
DO WHILE lnSeqNum <= n
    * The FetchSingleBd method was introduced in v9.5.0.76
    lnSuccess = loImap.FetchSingleBd(lnSeqNum,lnBUid,loMimeData)
    IF (lnSuccess <> 1) THEN
        ? loImap.LastErrorText
        RELEASE loImap
        RELEASE loDkim
        RELEASE loJson
        RELEASE loMimeData
        CANCEL
    ENDIF

    * Get the number of DKIM-Signature headers.
    lnNumDkim = loDkim.NumDkimSigs(loMimeData)

    * Verify each..
    j = 0
    DO WHILE j < lnNumDkim
        ? "------ DKIM Signature " + STR(j)

        lnSuccess = loDkim.DkimVerify(j,loMimeData)
        IF (lnSuccess <> 1) THEN
            ? "Not valid."
        ELSE
            ? "valid."
        ENDIF

        * Show the additional information about the signature verification
        loJson.Load(loDkim.VerifyInfo)
        ? loJson.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
    ENDDO
    lnSeqNum = lnSeqNum + 1
ENDDO

lnSuccess = loImap.Disconnect()

RELEASE loImap
RELEASE loDkim
RELEASE loJson
RELEASE loMimeData