Using variable extractor feature i have extracted the email id from a json and created a variable using a name 'Username' as mentioned in the screenshot.
How do i now pass multiple email's into this variable?
I'm not sure to understand your question. Do you want to pass multiple email's at the same time or a different one each time the POST request is executed?
If you extracted your email that means that it's coming from the server. But have you entered that email address as login and so i'm wondering if your goal is more that you would like to use a different login for each user?
Could you clarify a bit b/c i'm not sure that you are doing the right thing depending on your goal?