Add optional support for Dkim signing

[chaopeng]

extends Mailer to add sendDKIMMail()

[bbottema]

?

[chaopeng]

I saw a log: Providing access to Session instance for emergency fall-back scenario. Please let us know why you need it. I extends org.codemonkey.simplejavamail.Mailer and add a function to send DKIM mail. it need to convert the Message to DKIMMessage.

public final void sendDKIMMail(final Email email) throws MailException {
    if (validate(email)) {
        try {
            // fill and send wrapped mime message parts
            Message message = produceMimeMessage(email, getSession());
            convertToDKIMMessage(message, ...);
            message.saveChanges(); // some headers and id's will be set for this specific message
            Transport transport = getSession().getTransport();
            try {
                transport.connect();
                transport.sendMessage(message, message.getAllRecipients());
            } finally {
                transport.close();
            }
        } catch (final UnsupportedEncodingException e) {
            logger.error(e.getMessage(), e);
            throw new MailException(String.format("Encoding not accepted: %s", e.getMessage()), e);
        } catch (final MessagingException e) {
            logger.error(e.getMessage(), e);
            throw new MailException(String.format("Generic error: %s", e.getMessage()), e);
        }
    }
}

[bbottema]

Ahh, alright. Perhaps Session session should have been protected instead of private, so that you can reference it directly in subclasses instead of through the bean getter method. Then you won't get that warning log.

Btw, what is convertToDKIMMessage? Is that something this library might benefit from?

[chaopeng]

convertToDKIMMessage is a function to add DKIM signature to mail. I am using https://github.com/markenwerk/java-utils-mail-dkim to help me do this. I think it is good to add this to simple-java-mail.

[bbottema]

Will you share your implementation? I'm not really familiar with DKIM.

[bbottema]

What about this, @chaopeng:

Email email = new Email();
email.sign(dkimPrivateKeyFileForSender, signingDomain, selector);

Which throws an exception if DkimSigner is missing on the classpath, making the maven dependency on Dkim optional.

[chaopeng]

Thank you @bbottema . maybe the method also support byte[]/String as key is better.

[bbottema]

@chaopeng, what would be the content of that? Would it be the key itself, or a filepath to the key?

[chaopeng]

the string/ byte[] will be the key.

[bbottema]

Found this library as well: https://github.com/usrflo/DKIM-for-JavaMail

/edit: I just noticed that your reference is actually a fork on this one. I'm not sure which would be better, but the fork has been updated more recently.