接收退件通知

如要收到電子郵件的退信通知，您需要設定應用程式來啟用退信通知，並在應用程式中處理收到的通知。

設定應用程式的電子郵件退信通知

根據預設，對於無法傳送的電子郵件，應用程式不會接收退信通知。如要啟用傳入退信通知服務，您必須修改應用程式的 appengine-web.xml 和 web.xml 設定檔。

修改 appengine-web.xml，新增 inbound-services 區段，啟用內送退信服務：

<inbound-services>
  <!-- Used to handle incoming mail. -->
  <service>mail</service>
  <!-- Used to handle bounced mail notifications. -->
  <service>mail_bounce</service>
</inbound-services>

請按照下列方式，將退信網址 /_ah/bounce 對應至退信處理 Servlet，藉此修改 web.xml：

<servlet>
  <servlet-name>bouncehandler</servlet-name>
  <servlet-class>com.example.appengine.mail.BounceHandlerServlet</servlet-class>
</servlet>
<servlet-mapping>
  <servlet-name>bouncehandler</servlet-name>
  <url-pattern>/_ah/bounce</url-pattern>
</servlet-mapping>
<security-constraint>
  <web-resource-collection>
    <web-resource-name>bounce</web-resource-name>
    <url-pattern>/_ah/bounce</url-pattern>
  </web-resource-collection>
  <auth-constraint>
    <role-name>admin</role-name>
  </auth-constraint>
</security-constraint>

處理退信通知

JavaMail API 包含 BounceNotificationParser 類別，您可以使用這個類別來剖析收到的退信通知，如下所示：

import com.google.appengine.api.mail.BounceNotification;
import com.google.appengine.api.mail.BounceNotificationParser;

import java.io.IOException;
import java.util.logging.Logger;
import javax.mail.MessagingException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class BounceHandlerServlet extends HttpServlet {

  private static final Logger log = Logger.getLogger(BounceHandlerServlet.class.getName());

  @Override
  public void doPost(HttpServletRequest req, HttpServletResponse resp) throws IOException {
    try {
      BounceNotification bounce = BounceNotificationParser.parse(req);
      log.warning("Bounced email notification.");
      // The following data is available in a BounceNotification object
      // bounce.getOriginal().getFrom() 
      // bounce.getOriginal().getTo() 
      // bounce.getOriginal().getSubject() 
      // bounce.getOriginal().getText() 
      // bounce.getNotification().getFrom() 
      // bounce.getNotification().getTo() 
      // bounce.getNotification().getSubject() 
      // bounce.getNotification().getText() 
      // ...
    } catch (MessagingException e) {
    // ...
    }
  }
}