logback-android/src/main/java/ch/qos/logback/classic/net/SMTPAppender.java
protected void subAppend(CyclicBuffer<ILoggingEvent> cb, ILoggingEvent event) {
    if(includeCallerData) {
      event.getCallerData();
    }
    event.prepareForDeferredProcessing();
    cb.add(event);
  }
protected void subAppend(CyclicBuffer<ILoggingEvent> cb, ILoggingEvent event) {
    if(includeCallerData) {
      event.getCallerData();
    }
    event.prepareForDeferredProcessing();
    cb.add(event);
  }
Perform SMTPAppender specific appending actions, mainly adding the event to
a cyclic buffer.