Thanks David.. However I figure out there's a simpler solution to my problem (probably I didn't explain it very clearly in my initial post), so here is the update in case someone else run into the same scenario:
So I am still using the Recipient table (i.e. no new table is created), but obviously I still needed to extend the recipient table.
And then when it comes to data import, use Enrichment to 'Add data', and then define 'A link'. Select 'Define a collection' as the link type. Select 'Database schema' and 'nms:recipient' as the Target schema.
Next step is to 'Use a simple join'. Then in the Join conditions:
- Add email_address from the source file under Source column, and then '@email' in the Target column.
- Add the internal name of the recipient folder to the Source column, and then '[folder/@name] in the Target column. ---> this is the key step, as it tells AC to check if this email address exist in this specific recipient folder or not. If it doesn't, even if the same email can be found in other recipient folders across the same instance, it will still insert as a new record in this recipient folder. And this is what I need.
Then after Enrichment, add the Update data activity. Make sure the Record identification is set to 'Using reconciliation keys' and add both folder name and email in the Keys for finding records list.
So the end result is that if abc@test.com come onboard, AC will check if this email exists in the TEST01 recipient folder. If it does not, it will insert it, even though TEST02 recipient folders contains abc@test.com in the same AC instance.
Hope this helps.