Java

Verify DKIM-Signature Headers in Downloaded Email

See more DKIM / DomainKey Examples

Downloads email from an IMAP server and verifies the DKIM-Signature header(s) in each email, if present. Chilkat2 Java

import com.chilkatsoft.chilkat2.BinData;
import com.chilkatsoft.chilkat2.ChilkatException;
import com.chilkatsoft.chilkat2.Dkim;
import com.chilkatsoft.chilkat2.Imap;
import com.chilkatsoft.chilkat2.JsonObject;

public class ChilkatExample {

    public static void main(String[] args) {
        // This example requires the Chilkat API to have been previously unlocked.
        // See Global Unlock Sample for sample code.

        Imap imap = new Imap();

        // Connect to an IMAP server, login, select mailbox..
        // Use TLS
        imap.setSsl(true);
        imap.setPort(993);
        try {
            imap.connect("imap.example.com");
            imap.login("myLogin", "myPassword");
            imap.selectMailbox("Inbox");
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            return;
        }

        Dkim dkim = new Dkim();

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

        // Download emails by sequence numbers (not UIDs).
        boolean bUid = false;
        int j = 0;
        int n = imap.getNumMessages();
        if (n > 10) {
            n = 10;
        }

        JsonObject json = new JsonObject();
        json.setEmitCompact(false);

        // To verify DKIM-Signature headers, we need the exact unmodified MIME bytes of each email.
        BinData mimeData = new BinData();
        int seqNum = 1;
        while (seqNum <= n) {
            // The FetchSingleBd method was introduced in v9.5.0.76
            try {
                imap.fetchSingleBd(seqNum, bUid, mimeData);
            } catch (ChilkatException e) {
                System.out.println(e.getLastErrorText());
                return;
            }

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

            // Verify each..
            j = 0;
            while (j < numDkim) {
                System.out.println("------ DKIM Signature " + j);

                try {
                    dkim.dkimVerify(j, mimeData);
                    System.out.println("valid.");
                } catch (ChilkatException e) {
                    System.out.println("Not valid.");
                }

                // Show the additional information about the signature verification
                json.load(dkim.getVerifyInfo());
                System.out.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;
        }

        imap.disconnect();
    }
}