Notice: This is only my reasoning
In the BigTable, Row Key is a email address, a unique identifier and also a Receiver.
From: Cc:
================================================================================================================
edwardyoon@apache.org From:edward@udanax.org <"Edward J. Yoon"> Cc:hama-dev@incubator.apache.org <"hama">
Cc:chanwit@gmail.com <"Chanwit">
...
From:chanwit@gmail.com <"Chanwit">
Subject: Content: Address-Book: ...
================================================================================================================
<"Hello, I'm ed"> <"This is a content"> Address-Book:doug@apache.org <"Doug Cutting"> ...
Address-Book:channy@gmail.com <"Channy Yoon">
...
Social Email Graph
Notice: It is also only my reasoning