(Ruby) 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 Ruby Downloads install from rubygems.org gem install chilkat or download... Ruby Library for Windows, MacOS, Linux, Alpine Linux

require '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(true)
imap.put_Port(993)
success = imap.Connect("imap.someMailServer.com")
if (success == true)
    success = imap.Login("myLogin","myPassword")
    if (success == true)
        success = imap.SelectMailbox("Inbox")
    end

end

if (success != true)
    print imap.lastErrorText() + "\n";
    exit
end

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 = false

n = imap.get_NumMessages()
if (n > 10)
    n = 10
end

json = Chilkat::CkJsonObject.new()
json.put_EmitCompact(false)

# 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 != true)
        print imap.lastErrorText() + "\n";
        exit
    end

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

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

        success = dkim.DkimVerify(j,mimeData)
        if (success != true)
            print "Not valid." + "\n";
        else
            print "valid." + "\n";
        end

        # Show the additional information about the signature verification
        json.Load(dkim.verifyInfo())
        print json.emit() + "\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
    end
    seqNum = seqNum + 1
end

success = imap.Disconnect()