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"> ...