send_email_4.java

@Value
@Accessors(fluent = true)
public class Payload {
    private final String body;
}

@Value
@Accessors(fluent = true)
public class EmailMessage {
    private final Email email;
    private final Payload payload;
}

public class EmailSender {
    public SendingResult send(EmailMessage message) {
        return new SendingResult(doSend(message.email(), message.payload().body()));
    }
}