Hi Sanjana,
I think the document Automating Rate Updates in DSM and BRFPlus may answer your questions. Here you have a code snippet how to fetch the data stored in a decision table. Although the document is about the update you can see on page 8 how to get the row data. On page 9 you will see how to extract the data from the single cells (there is quite some de-referencing to do). If you finally have the data you can directly put it into an internal table.
If it just comes for the backup, it might also be an option to create a "backup" application in BRFplus and just copy your decision table to that application. This for sure does not fulfill the requirement concerning the mail, but saving the data into an internal table might be quite challenging when you think about more sophisticated data in the decision table (ranges within cells or even other
expressions)
Hope that helps
Best Regards
Christian