Look for the qa_db_user_create() function in the file at \qa-includes\db\users.php
Within that function, you have to write a code to insert a user record with default newsletter status of '1' to the usermetas table immediately after the if-else conditions for inserting their data into the users table.
When you're done, the concluding part of that function should look like screenshot below:
![](https://www.question2answer.org/qa/?qa=blob&qa_blobid=9313160827911782327)
This will automatically subscribe new users that register on your website to the newsletter. For the existing users, you'll have to reference their ids on the usermetas table manually. Goodluck!