接收退信通知

要接收电子邮件退信通知，您需要将应用配置为启用退信通知，并需要在应用中处理传入通知。

配置应用以接收电子邮件退信通知

默认情况下，应用不接收无法递送的电子邮件的退信通知。要启用传入退信通知服务，您需要修改应用的 appengine-web.xml 和 web.xml 配置文件。

通过添加 inbound-services 部分修改 appengine-web.xml，以启用传入退信服务：

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

通过将退信网址 /_ah/bounce 映射到退信处理 Servlet 来修改 web.xml，如下所示：

<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>

处理退信通知

JavaMail API 包含 BounceNotificationParser 类，此类用于解析如下所示的传入退信通知：

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) {
    // ...
    }
  }
}