(Go) 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 Go Downloads Go Package for Windows, MacOS, Linux, Alpine Linux, Solaris

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

    imap := chilkat.NewImap()

    // Connect to an IMAP server, login, select mailbox..
    // Use TLS 
    imap.SetSsl(true)
    imap.SetPort(993)
    success := imap.Connect("imap.someMailServer.com")
    if success == true {
        success = imap.Login("myLogin","myPassword")
        if success == true {
            success = imap.SelectMailbox("Inbox")
        }

    }

    if success != true {
        fmt.Println(imap.LastErrorText())
        imap.DisposeImap()
        return
    }

    dkim := chilkat.NewDkim()

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

    // Download emails by sequence numbers (not UIDs).
    bUid := false
    var seqNum int
    var j int
    n := imap.NumMessages()
    if n > 10 {
        n = 10
    }

    json := chilkat.NewJsonObject()
    json.SetEmitCompact(false)

    // To verify DKIM-Signature headers, we need the exact unmodified MIME bytes of each email.
    mimeData := chilkat.NewBinData()
    seqNum = 1
    for seqNum <= n {
        // The FetchSingleBd method was introduced in v9.5.0.76
        success = imap.FetchSingleBd(seqNum,bUid,mimeData)
        if success != true {
            fmt.Println(imap.LastErrorText())
            imap.DisposeImap()
            dkim.DisposeDkim()
            json.DisposeJsonObject()
            mimeData.DisposeBinData()
            return
        }

        // Get the number of DKIM-Signature headers.
        numDkim := dkim.NumDkimSigs(mimeData)

        // Verify each..
        j = 0
        for j < numDkim {
            fmt.Println("------ DKIM Signature ", j)

            success = dkim.DkimVerify(j,mimeData)
            if success != true {
                fmt.Println("Not valid.")
            }
            else {
                fmt.Println("valid.")
            }

            // Show the additional information about the signature verification
            json.Load(dkim.VerifyInfo())
            fmt.Println(*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
        }

        seqNum = seqNum + 1
    }

    success = imap.Disconnect()

    imap.DisposeImap()
    dkim.DisposeDkim()
    json.DisposeJsonObject()
    mimeData.DisposeBinData()