Is there a possibility to set spring integration mail inbound adapter flags after handling the message?

Question

Intro:
We're currently using the spring mail integration to receive and send emails which works without flaws if there's no exception such as a connection error to the exchange server or the database.

These mails come in as Messages and are passed to a handler method which will parse the MimeMessage to a custom mail data object. JPA saves those entities as the last step to our database.

Question/Problem:
There's a problem if the database is down or the mail can't be processed for any other reason, as the IntegrationFlow will still mark it as /SEEN once the message gets passed to the handler.

Setting this flag to false won't fix our problem, because we want Spring to set the /SEEN flag if the mail is processed and saved correctly

shouldMarkMessagesAsRead(false) 

Searching for:
Would there be a possibility to set flags AFTER successfully saving the mail to the database?
We'd like to process the failed email again after the cause for the responsible error is fixed, which won't work as long Spring marks them as /SEEN no matter the result.

Reference:
The messages comes in and gets passed to the handler which will parse the mail and execute the CRUD-Repository save(mailDAO) method. The handleMimeMessage() is more or less just a mapper.

@Bean
fun imapIdleFlow(imapProperties: ImapProperties): IntegrationFlow {
    imapProperties.username.let { URLEncoder.encode(it, charset) }
    return IntegrationFlows
        .from(
            Mail.imapIdleAdapter(
                ImapMailReceiver("imap://${imapProperties.username}:${imapProperties.password}@${imapProperties.host}/Inbox")
                    .apply {
                        setSimpleContent(true)
                        setJavaMailProperties(imapProperties.properties.toProperties())
                    })
                .autoStartup(true)
                .shouldReconnectAutomatically(true)
        )
        .handle(this::handleMimeMessage)
        .get()
}

Is it even possible to mark the messages in the same flow afterward as you need to access the exchange a second time or would I need a second flow to get and flag the same mail?

Answer 1

I think it is possible with something like transaction synchronization: https://docs.spring.io/spring-integration/reference/html/mail.html#mail-tx-sync

So, you set transactional(TransactionManager transactionManager) on that Mail.imapIdleAdapter to the JpaTransactionManager to start transaction from this IMAP Idle channel adapter and propagate it to your handleMimeMessage() where you do those JPA saves.

Plus you add:

/**
 * Configure a {@link TransactionSynchronizationFactory}. Usually used to synchronize
 * message deletion with some external transaction manager.
 * @param transactionSynchronizationFactory the transactionSynchronizationFactory.
 * @return the spec.
 */
public ImapIdleChannelAdapterSpec transactionSynchronizationFactory(
        TransactionSynchronizationFactory transactionSynchronizationFactory) {

To react for commit and rollback of the mentioned transaction.

The DefaultTransactionSynchronizationFactory with some TransactionSynchronizationProcessor impl can give you a desired behavior, where you take a Message and its payload from the provided IntegrationResourceHolder and perform something like message.setFlag(Flag.SEEN, true); on the MimeMessage.

You may consider to use the mentioned in docs an ExpressionEvaluatingTransactionSynchronizationProcessor.

To avoid folder reopening, you may consider to use a public ImapIdleChannelAdapterSpec autoCloseFolder(boolean autoCloseFolder) { with a false option. You need to consider to close it in that TX sync impl or some other way.