20. Mail Support

20.1 Mail-Sending Channel Adapter

Spring Integration provides support for outbound email with the MailSendingMessageHandler. It delegates to a configured instance of Spring's JavaMailSender:

 JavaMailSender mailSender = context.getBean("mailSender", JavaMailSender.class);

 MailSendingMessageHandler mailSendingHandler = new MailSendingMessageHandler(mailSender);

MailSendingMessageHandler has various mapping strategies that use Spring's MailMessage abstraction. If the received Message's payload is already a MailMessage instance, it will be sent directly. Therefore, it is generally recommended to precede this consumer with a Transformer for non-trivial MailMessage construction requirements. However, a few simple Message mapping strategies are supported out-of-the-box. For example, if the message payload is a byte array, then that will be mapped to an attachment. For simple text-based emails, you can provide a String-based Message payload. In that case, a MailMessage will be created with that String as the text content. If you are working with a Message payload type whose toString() method returns appropriate mail text content, then consider adding Spring Integration's ObjectToStringTransformer prior to the outbound Mail adapter (see the example within the section called “Configuring Transformer with XML” for more detail).

The outbound MailMessage may also be configured with certain values from the MessageHeaders. If available, values will be mapped to the outbound mail's properties, such as the recipients (TO, CC, and BCC), the from/reply-to, and the subject. The header names are defined by the following constants:

 MailHeaders.SUBJECT
 MailHeaders.TO
 MailHeaders.CC
 MailHeaders.BCC
 MailHeaders.FROM
 MailHeaders.REPLY_TO

[Note]Note
MailHeaders also allows you to override corresponding MailMessage values. For example: If MailMessage.to is set to 'foo@bar.com' and MailHeaders.TO Message header is provided it will take precedence and override the corresponding value in MailMessage

20.2 Mail-Receiving Channel Adapter

Spring Integration also provides support for inbound email with the MailReceivingMessageSource. It delegates to a configured instance of Spring Integration's own MailReceiver interface, and there are two implementations: Pop3MailReceiver and ImapMailReceiver. The easiest way to instantiate either of these is by passing the 'uri' for a Mail store to the receiver's constructor. For example:

 MailReceiver receiver = new Pop3MailReceiver("pop3://usr:pwd@localhost/INBOX");

Another option for receiving mail is the IMAP "idle" command (if supported by the mail server you are using). Spring Integration provides the ImapIdleChannelAdapter which is itself a Message-producing endpoint. It delegates to an instance of the ImapMailReceiver but enables asynchronous reception of Mail Messages. There are examples in the next section of configuring both types of inbound Channel Adapter with Spring Integration's namespace support in the 'mail' schema.

20.3 Mail Namespace Support

Spring Integration provides a namespace for mail-related configuration. To use it, configure the following schema locations.

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:int-mail="http://www.springframework.org/schema/integration/mail"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
            http://www.springframework.org/schema/beans/spring-beans.xsd
            http://www.springframework.org/schema/integration/mail
            http://www.springframework.org/schema/integration/mail/spring-integration-mail.xsd">

To configure an outbound Channel Adapter, provide the channel to receive from, and the MailSender:

<int-mail:outbound-channel-adapter channel="outboundMail"
                              mail-sender="mailSender"/>

Alternatively, provide the host, username, and password:

<int-mail:outbound-channel-adapter channel="outboundMail"
                              host="somehost" username="someuser" password="somepassword"/>

[Note]Note
Keep in mind, as with any outbound Channel Adapter, if the referenced channel is a PollableChannel, a <poller> sub-element should be provided with either an interval-trigger or cron-trigger.

To configure an Inbound Channel Adapter, you have the choice between polling or event-driven (assuming your mail server supports IMAP IDLE - if not, then polling is the only option). A polling Channel Adapter simply requires the store URI and the channel to send inbound Messages to. The URI may begin with "pop3" or "imap":

<int-mail:inbound-channel-adapter id="imapAdapter"
      store-uri="imaps://[username]:[password]@imap.gmail.com/INBOX"
      java-mail-properties="javaMailProperties"
      channel="recieveChannel"
      should-delete-messages="true"
      should-mark-messages-as-read="true"
      auto-startup="true">
      <int:poller max-messages-per-poll="1" fixed-rate="5000"/>
</int-mail:inbound-channel-adapter>

If you do have IMAP idle support, then you may want to configure the "imap-idle-channel-adapter" element instead. Since the "idle" command enables event-driven notifications, no poller is necessary for this adapter. It will send a Message to the specified channel as soon as it receives the notification that new mail is available:

<int-mail:imap-idle-channel-adapter id="customAdapter"
      store-uri="imaps://[username]:[password]@imap.gmail.com/INBOX"
      channel="recieveChannel"
      auto-startup="true"
      should-delete-messages="false"
      should-mark-messages-as-read="true"
      java-mail-properties="javaMailProperties"/>

... where javaMailProperties could be provided by creating and populating a regular java.utils.Properties object. For example via util namespace provided by Spring.

[Important]Important
If your username contains the '@' character use '%40' instead of '@' to avoid parsing errors from the underlying JavaMail API.

<util:properties id="javaMailProperties">
  <prop key="mail.imap.socketFactory.class">javax.net.ssl.SSLSocketFactory</prop>
  <prop key="mail.imap.socketFactory.fallback">false</prop>
  <prop key="mail.store.protocol">imaps</prop>
  <prop key="mail.debug">false</prop>
</util:properties>

By default, the ImapMailReceiver will search for Messages based on the default SearchTerm which is All mails that are RECENT (if supported), that are NOT ANSWERED, that are NOT DELETED, that are NOT SEEN and have not been processed by this mail receiver (enabled by the use of the custom USER flag or simply NOT FLAGGED if not supported). Since version 2.2, the SearchTerm used by the ImapMailReceiver is fully configurable via the SearchTermStrategy which you can inject via the search-term-strategy attribute. SearchTermStrategy is a simple strategy interface with a single method that allows you to create an instance of the SearchTerm that will be used by the ImapMailReceiver.

public interface SearchTermStrategy {

	SearchTerm generateSearchTerm(Flags supportedFlags, Folder folder);

}

For example:

<mail:imap-idle-channel-adapter id="customAdapter"
			store-uri="imap:foo"
			. . .	
			search-term-strategy="searchTermStrategy"/>
			
<bean id="searchTermStrategy" class="org.springframework.integration.mail.config.ImapIdleChannelAdapterParserTests.TestSearchTermStrategy"/>

In the above example instead of relying on the default SearchTermStrategy the TestSearchTermStrategy will be used instead

IMAP IDLE and lost connection

When using IMAP IDLE channel adapter there might be situations where connection to the server may be lost (e.g., network failure) and since Java Mail documentation explicitly states that the actual IMAP API is EXPERIMENTAL it is important to understand the differences in the API and how to deal with them when configuring IMAP IDLE adapters. Currently Spring Integration Mail adapters was tested with Java Mail 1.4.1 and Java Mail 1.4.3 and depending on which one is used special attention must be payed to some of the java mail properties that needs to be set with regard to auto-reconnect.

The following behavior was observed with GMAIL but should provide you with some tips on how to solve re-connect issue with other providers, however feedback is always welcome. Again, below notes are based on GMAIL.

With Java Mail 1.4.1 if mail.imaps.timeout property is set for a relatively short period of time (e.g., ~ 5 min) then IMAPFolder.idle() will throw FolderClosedException after this timeout. However if this property is not set (should be indefinite) the behavior that was observed is that IMAPFolder.idle() method never returns nor it throws an exception. It will however reconnect automatically if connection was lost for a short period of time (e.g., under 10 min), but if connection was lost for a long period of time (e.g., over 10 min), then IMAPFolder.idle() will not throw FolderClosedException nor it will re-establish connection and will remain in the blocked state indefinitely, thus leaving you no possibility to reconnect without restarting the adapter. So the only way to make re-connect to work with Java Mail 1.4.1 is to set mail.imaps.timeout property explicitly to some value, but it also means that such value shoudl be relatively short (under 10 min) and the connection should be re-estabished relatively quickly. Again, it may be different with other providers. With Java Mail 1.4.3 there was significant improvements to the API ensuring that there will always be a condition which will force IMAPFolder.idle() method to return via StoreClosedException or FolderClosedException or simply return, thus allowing us to proceed with auto-reconnect. Currently auto-reconnect will run infinitely making attempts to reconnect every 10 sec.

[Important]Important
In both configurations channel and should-delete-messages are the REQUIRED     attributes. The important thing to understand is why should-delete-messages is required.     The issue is with the POP3 protocol, which does NOT have any knowledge of messages that were READ. It can only know what's been read      within a single session. This means that when your POP3 mail adapter is running, emails are successfully consumed as as they become available during each poll     and no single email message will be delivered more then once. However, as soon as you restart your adapter and begin a new session     all the email messages that might have been retrieved in the previous session will be retrieved again. That is the nature of POP3. Some might argue     that should-delete-messages should be TRUE by default. In other words, there are two valid and mutually exclusive use cases      which make it very hard to pick a single "best" default. You may want to configure your adapter as the only email receiver in which     case you want to be able to restart such adapter without fear that messages that were delivered before will not be redelivered again.      In this case setting should-delete-messages to TRUE would make most sense. However, you may have another use case where      you may want to have multiple adapters that simply monitor email servers and their content. In other words you just want to 'peek but not touch'.      Then setting should-delete-messages to FALSE would be much more appropriate. So since it is hard to choose what should be     the right default value for the should-delete-messages attribute, we simply made it a required attribute, to be set by the user. Leaving it up to the user also means, you will be less likely to end up with unintended behavior.
[Note]Note
When configuring a polling email adapter's should-mark-messages-as-read attribute, be aware of the protocol you are configuring to retrieve messages. For example POP3 does not support this flag which means setting it to either value will have no effect as messages will NOT be marked as read.
[Important]Important

It is important to understand that that these actions (marking messages read, and deleting messages) are performed after the messages are received, but before they are processed. This can cause messages to be lost.

You may wish to consider using transaction synchronization instead - see Section 20.5, “Transaction Synchronization”

When using the namespace support, a header-enricher Message Transformer is also available. This simplifies the application of the headers mentioned above to any Message prior to sending to the Mail-sending Channel Adapter.

<int-mail:header-enricher subject="Example Mail"
                     to="to@example.org"
                     cc="cc@example.org"
                     bcc="bcc@example.org"
                     from="from@example.org"
                     reply-to="replyTo@example.org"
                     overwrite="false"/>

Finally, the <imap-idle-channel-adapter/> also accepts the 'error-channel' attribute. If a downstream exception is thrown and an 'error-channel' is specified, a MessagingException message containing the failed message and original exception, will be sent to this channel. Otherwise, if the downstream channels are synchronous, any such exception will simply be logged as a warning by the channel adapter.

20.4 Email Message Filtering

Very often you may encounter a requirement to filter incoming messages (e.g., You want to only read emails that have 'Spring Integration' in the Subject line). This could be easily accomplished by connecting Inbound Mail adapter with an expression-based Filter. Although it would work, there is a downside to this approach. Since messages would be filtered after going through inbound mail adapter all such messages would be marked as read (SEEN) or Un-read (depending on the value of should-mark-messages-as-read attribute). However in reality what would be more useful is to mark messages as SEEN only if they passed the filtering criteria. This is very similar to looking at your email client while scrolling through all the messages in the preview pane, but only flagging messages as SEEN that were actually opened and read.

In Spring Integration 2.0.4 we've introduced mail-filter-expression attribute on inbound-channel-adapter and imap-idle-channel-adapter. This attribute allows you to provide an expression which is a combination of SpEL and Regular Expression. For example if you would like to read only emails that contain 'Spring Integration' in the Subject line, you would configure mail-filter-expression attribute like this this: mail-filter-expression="subject matches '(?i).*Spring Integration.*"

Since javax.mail.internet.MimeMessage is the root context of SpEL Evaluation Context, you can filter on any value available through MimeMessage including the actual body of the message. This one is particularly important since reading the body of the message would typically result in such message to be marked as SEEN by default, but since we now setting PEAK flag of every incomming message to 'true', only messages that were explicitly marked as SEEN will be seen as read.

So in the below example only messages that match the filter expression will be output by this adapter and only those messages will be marked as SEEN. In this case based on the mail-filter-expression only messages that contain 'Spring Integration' in the subject line will be produced by this adapter.

<int-mail:imap-idle-channel-adapter id="customAdapter"
	store-uri="imaps://some_google_address:${password}@imap.gmail.com/INBOX"
	channel="receiveChannel"	
	should-mark-messages-as-read="true"
	java-mail-properties="javaMailProperties"
	mail-filter-expression="subject matches '(?i).*Spring Integration.*'"/>

Another reasonable question is what happens on the next poll, or idle event, or what happens when such adapter is restarted. Will there be a potential duplication of massages to be filtered? In other words if on the last retrieval where you had 5 new messages and only 1 passed the filter what would happen with the other 4. Would they go through the filtering logic again on the next poll or idle? After all they were not marked as SEEN. The actual answer is no. They would not be subject of duplicate processing due to another flag (RECENT) that is set by the Email server and is used by Spring Integration mail search filter. Folder implementations set this flag to indicate that this message is new to this folder, that is, it has arrived since the last time this folder was opened. In other while our adapter may peek at the email it also lets the email server know that such email was touched and therefore will be marked as RECENT by the email server.

20.5 Transaction Synchronization

Transaction synchronization for inbound adapters allows you to take different actions after a transaction commits, or rolls back. Transaction synchronization is enabled by adding a <transactional/> element to the poller for the polled <inbound-adapter/>, or to the <imap-idle-inbound-adapter/>. Even if there is no 'real' transaction involved, you can still enable this feature by using a PseudoTransactionManager with the <transactional/> element. For more information, see Section B.3, “Transaction Synchronization”.

Because of the many different mail servers, and specifically the limitations that some have, at this time we only provide a strategy for these transaction synchronizations. You can send the messages to some other Spring Integration components, or invoke a custom bean to perform some action. For example, to move an IMAP message to a different folder after the transaction commits, you might use something similar to the following:

<int-mail:imap-idle-channel-adapter id="customAdapter"
			store-uri="imaps://foo.com:password@imap.foo.com/INBOX"
			channel="receiveChannel"
			auto-startup="true"
			should-delete-messages="false"		
			java-mail-properties="javaMailProperties">
	<int:transactional synchronization-factory="syncFactory"/>
</int-mail:imap-idle-channel-adapter>

<int:transaction-synchronization-factory id="syncFactory">
	<int:after-commit expression="@syncProcessor.process(payload)"/>
</int:transaction-synchronization-factory>

<bean id="syncProcessor" class="foo.bar.Mover"/>

public class Mover {

	public void process(MimeMessage message) throws Exception{
		Folder folder = message.getFolder();
		folder.open(Folder.READ_WRITE);
		String messageId = message.getMessageID();
		Message[] messages = folder.getMessages();
		FetchProfile contentsProfile = new FetchProfile();
		contentsProfile.add(FetchProfile.Item.ENVELOPE);
		contentsProfile.add(FetchProfile.Item.CONTENT_INFO);
		contentsProfile.add(FetchProfile.Item.FLAGS);
		folder.fetch(messages, contentsProfile);
		// find this message and mark for deletion
		for (int i = 0; i < messages.length; i++) {
			if (((MimeMessage) messages[i]).getMessageID().equals(messageId)) {
				messages[i].setFlag(Flags.Flag.DELETED, true);
				break;
			}
		}

		Folder fooFolder = store.getFolder("FOO"));
		fooFolder.appendMessages(new MimeMessage[]{message});
		folder.expunge();
		folder.close(true);
		fooFolder.close(false);
	}
}
[Important]Important
For the message to be still available for manipulation after the transaction, should-delete-messages must be set to 'false'.