(Java) Send DKIM Signed Email

Demonstrates how to create a simple email, add a DKIM signature, and send it.

Note: Requires version 9.0.3 or greater.

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import com.chilkatsoft.*;

public class ChilkatExample {

  static {
    try {
        System.loadLibrary("chilkat");
    } catch (UnsatisfiedLinkError e) {
      System.err.println("Native code library failed to load.\n" + e);
      System.exit(1);
    }
  }

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

    // The mailman object is used for sending and receiving email.
    CkMailMan mailman = new CkMailMan();

    // The dkim object is used for creating the DKIM signature.
    CkDkim dkim = new CkDkim();

    // Set the SMTP server.
    mailman.put_SmtpHost("smtp.chilkatsoft.com");

    // Set the SMTP login/password (if required)
    mailman.put_SmtpUsername("myLogin");
    mailman.put_SmtpPassword("myPassword");
    // Set the SmtpPort if your SMTP server uses an alternative port (default = 25)
    mailman.put_SmtpPort(587);

    // Create a new email object
    CkEmail email = new CkEmail();

    email.put_Subject("This is a test");
    email.put_Body("This is a test");
    email.put_From("Chilkat Support <support@chilkatsoft.com>");
    // We'll send the email to a Yahoo email account.  It is then
    // possible to view the full headers within the Yahoo email
    // interface to see if the DKIM signature was accepted.
    boolean success = email.AddTo("Chilkat Software","chilkat_software@yahoo.com");
    success = email.AddTo("Chilkat Admin","admin@chilkatsoft.com");

    // When sending an email with a DKIM signature, the MIME
    // of the email must not be modified (in significant ways) prior to
    // or during the sending process.  Therefore, the MIME of the
    // email is assembled, the DKIM signature is added, and then
    // SendMimeBytes is called to send the email.

    // Get the MIME of the email.  Calling RenderToMimeBytes 
    // causes the email to be signed and/or encrypted if those options
    // have been selected.  The MIME returned by RenderToMimeBytes
    // is the exact MIME that would've been sent if SendEmail was
    // called.  We'll add a DKIM signature header to this MIME and then send...
    CkByteData mimeData = new CkByteData();
    success = mailman.RenderToMimeBytes(email,mimeData);
    if (success != true) {
        System.out.println(mailman.lastErrorText());
        return;
        }

    // To create a DKIM signature for email (i.e. MIME),
    // you'll need to provide the following:
    // (1) An RSA private key in any common file format.
    // (2) The domain name (typically the same domain
    // as the sender of an email).
    // (3) A selector for the domain name -- an arbitrary string
    // to identify the matching public key in DNS.

    // To allow an email recipient to verify the DKIM signature via an
    // external email client supporting DKIM or using other software,
    // you will need to create a DNS record with the selector
    // and matching public key.  This example does not provide
    // information about DKIM DNS record creation.  
    // (Chilkat does not provide an API for creating DNS records.  
    // Creating the DKIM DNS record is something you would do
    // manually.)

    // Set the domain and selector:
    // You'll need to provide your own values here..
    dkim.put_DkimDomain("chilkatsoft.com");
    dkim.put_DkimSelector("brisbane");

    // Load a private key from any common RSA private key
    // format, such as DER, PKCS8, PEM, XML, etc.
    // The LoadDkimPkFile method automatically detects
    // the file format and reads it appropriately.
    // If a password is not required, you'll still need to provide
    // a password string argument, but it is ignored.
    String password = "optionalPassword";
    CkPrivateKey privKey = new CkPrivateKey();
    success = privKey.LoadAnyFormatFile("myPrivateKey.pem",password);
    if (success != true) {
        System.out.println(privKey.lastErrorText());
        return;
        }

    success = dkim.SetDkimPrivateKey(privKey);
    if (success != true) {
        System.out.println(dkim.lastErrorText());
        return;
        }

    // Add the DKIM-Signature header and
    // returns the new MIME with DKIM-Signature added.
    CkByteData dkimSignedMime = new CkByteData();

    success = dkim.AddDkimSignature(mimeData,dkimSignedMime);
    if (success != true) {
        System.out.println(dkim.lastErrorText());
        return;
        }

    // Call SendMimeBytes to connect to the SMTP server and send.
    // The connection (i.e. session) to the SMTP server remains
    // open so that subsequent Send* calls may use the
    // same connection.  
    String strFrom = "support@chilkatsoft.com";
    // To send to multiple email addresses, the strTo should be set to a comma-separated
    // list of email addresses.
    String strTo = "chilkat_software@yahoo.com, admin@chilkatsoft.com";
    success = mailman.SendMimeBytes(strFrom,strTo,dkimSignedMime);
    if (success != true) {
        System.out.println(mailman.lastErrorText());
        return;
        }

    // Some SMTP servers do not actually send the email until 
    // the connection is closed.  In these cases, it is necessary to
    // call CloseSmtpConnection for the mail to be  sent.  
    // Most SMTP servers send the email immediately, and it is 
    // not required to close the connection.  We'll close it here
    // for the example:
    success = mailman.CloseSmtpConnection();
    if (success != true) {
        System.out.println("Connection to SMTP server not closed cleanly.");
        }

    System.out.println("DKIM Signed Mail Sent!");
  }
}