Hi Douglas,
Thanks for reply. Still i did not got the solution for finding where email text is stored in SAP tenant system. But i have checked one Business object(through SDK tool) "DocumentOutputRequest" which comes under "http://sap.com/xi/DocumentServices/Global" namespace. And it shows Electronic Message Body text. But when i tried to Edit it in QA screen it dosent allows me. But i think it is not the BO which saves stored email body text, it is the BO which shows all edited email body text and Created And Changed date.