SMTPServerExtension.java

public class SMTPServerExtension implements BeforeEachCallback, AfterEachCallback {

   private GreenMail smtpServer;
   private String hostname;
   private int port;

   public SMTPServerExtension() {
       this(25);
   }

   public SMTPServerExtension(int port) {
       this("localhost", port);
   }

   public SMTPServerExtension(String hostname, int port) {
       this.hostname = hostname;
       this.port = port;
   }

   public List<ExpectedMail> getMessages() {
       return Lists.newArrayList(smtpServer.getReceivedMessages()).stream()
           .parallel()
           .map(mimeMessage -> ExpectedMail.transformMimeMessage(mimeMessage)).collect(Collectors.toList());
   }


   @Override
   public void afterEach(ExtensionContext extensionContext) throws Exception {
       smtpServer.stop();
   }

   @Override
   public void beforeEach(ExtensionContext extensionContext) throws Exception {
       smtpServer = new GreenMail(new ServerSetup(port, hostname, "smtp"));
       smtpServer.start();
   }
}