(Node.js) 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.

Install Chilkat for Node.js and Electron using npm at Chilkat npm packages for Node.js Chilkat npm packages for Electron on Windows, Linux, MacOSX, and ARM

var os = require('os');
if (os.platform() == 'win32') {  
    if (os.arch() == 'ia32') {
        var chilkat = require('@chilkat/ck-node21-win-ia32');
    } else {
        var chilkat = require('@chilkat/ck-node21-win64'); 
    }
} else if (os.platform() == 'linux') {
    if (os.arch() == 'arm') {
        var chilkat = require('@chilkat/ck-node21-arm');
    } else if (os.arch() == 'x86') {
        var chilkat = require('@chilkat/ck-node21-linux32');
    } else {
        var chilkat = require('@chilkat/ck-node21-linux64');
    }
} else if (os.platform() == 'darwin') {
    if (os.arch() == 'arm64') {
        var chilkat = require('@chilkat/ck-node21-mac-m1');
    } else {
        var chilkat = require('@chilkat/ck-node21-macosx');
    }
}

function chilkatExample() {

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

    var imap = new chilkat.Imap();

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

    }

    if (success !== true) {
        console.log(imap.LastErrorText);
        return;
    }

    var dkim = 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).
    var bUid = false;
    var seqNum;
    var j;
    var n = imap.NumMessages;
    if (n > 10) {
        n = 10;
    }

    var json = new chilkat.JsonObject();
    json.EmitCompact = false;

    // To verify DKIM-Signature headers, we need the exact unmodified MIME bytes of each email.
    var mimeData = 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) {
            console.log(imap.LastErrorText);
            return;
        }

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

        // Verify each..
        j = 0;
        while (j < numDkim) {
            console.log("------ DKIM Signature " + j);

            success = dkim.DkimVerify(j,mimeData);
            if (success !== true) {
                console.log("Not valid.");
            }
            else {
                console.log("valid.");
            }

            // Show the additional information about the signature verification
            json.Load(dkim.VerifyInfo);
            console.log(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();

}

chilkatExample();