(Perl) 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 Perl Downloads Perl Module for Windows, MacOS, Linux, Alpine Linux, Solaris

use chilkat();

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

$imap = chilkat::CkImap->new();

# Connect to an IMAP server, login, select mailbox..
# Use TLS 
$imap->put_Ssl(1);
$imap->put_Port(993);
$success = $imap->Connect("imap.someMailServer.com");
if ($success == 1) {
    $success = $imap->Login("myLogin","myPassword");
    if ($success == 1) {
        $success = $imap->SelectMailbox("Inbox");
    }

}

if ($success != 1) {
    print $imap->lastErrorText() . "\r\n";
    exit;
}

$dkim = chilkat::CkDkim->new();

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

# Download emails by sequence numbers (not UIDs).
$bUid = 0;

$n = $imap->get_NumMessages();
if ($n > 10) {
    $n = 10;
}

$json = chilkat::CkJsonObject->new();
$json->put_EmitCompact(0);

# To verify DKIM-Signature headers, we need the exact unmodified MIME bytes of each email.
$mimeData = chilkat::CkBinData->new();
$seqNum = 1;
while ($seqNum <= $n) {
    # The FetchSingleBd method was introduced in v9.5.0.76
    $success = $imap->FetchSingleBd($seqNum,$bUid,$mimeData);
    if ($success != 1) {
        print $imap->lastErrorText() . "\r\n";
        exit;
    }

    # Get the number of DKIM-Signature headers.
    $numDkim = $dkim->NumDkimSigs($mimeData);

    # Verify each..
    $j = 0;
    while ($j < $numDkim) {
        print "------ DKIM Signature " . $j . "\r\n";

        $success = $dkim->DkimVerify($j,$mimeData);
        if ($success != 1) {
            print "Not valid." . "\r\n";
        }
        else {
            print "valid." . "\r\n";
        }

        # Show the additional information about the signature verification
        $json->Load($dkim->verifyInfo());
        print $json->emit() . "\r\n";

        # 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();