Hi @hktang,
The discussion is limited to being within OJS, and it is not sent outside of it. This thread explains some of the options have for notifications: [SOLVED] Different way to show Review contents to authors - #3 by Alejandra_Casas (please note this is for 3.1, but the premise is the same, and user options are under “notifications” under the user’s profile.
I will note, however, that there is work planned to change this in the upcoming version of OJS (3.4): Embed discussion content into the notification message body · Issue #6222 · pkp/pkp-lib · GitHub
-Roger
PKP team