explicit set an "optional" tag
diff --git a/Android.mk b/Android.mk
index 277d0e5..1fd0799 100644
--- a/Android.mk
+++ b/Android.mk
@@ -15,6 +15,8 @@
 LOCAL_PATH:= $(call my-dir)
 include $(CLEAR_VARS)
 
+LOCAL_MODULE_TAGS := optional
+
 LOCAL_SRC_FILES := $(call all-java-files-under, src)
 LOCAL_SRC_FILES += \
     src/com/android/exchange/IEmailService.aidl \