I wish to download all emails and put it within a .txt file. Then I want to send selected emails to selected people using any keywords in the email

[Taifun]

Make yourself familiar with SQL...
See this tutorial

Use gviz to get and query google sheet data

[gvizscreen1] Guide on how to use the google visualization API to get and query "public" google sheet data Use gviz to get and query google sheet data Note: this approach has been knocking around for years, e.g. https://puravidaapps.com/spreadsheet.php, but I have never seen it "properly" explained like this...

And the query language documentation Query Language Reference (Version 0.7)  |  Charts  |  Google for Developers

@S.V_Arul_Shiju

Display only the rows that contains the word UNIQUE ID OF JACK in any of its column.

Try this query (assiming there are only 2 columns A and B, for more columns add more OR statements):

SELECT * WHERE A CONTAINS '"UNIQUE ID OF JACK" OR B CONTAINS "UNIQUE ID OF JACK"

Taifun