Hi cho laiw17892104,
As per your initial post, "I was trying to generate one csv file dynamically for each recipient in AC server for the group of recipients.
After that tried to deliver the email to the group of 700+ people and attached this generated csv files."
Is there some time gap in between these two steps.
There could be a possibility that the file isn't generated when the Delivery is targeting initial set of Recipients. Later once its ready, other Recipients are targeted.
With a smaller Recipient set, the execution time turns out to be less, that could be the reason why file is quickly available to be sent to Recipients.
This could further be validated by performing 1-2 tests.
Try working with a list of 200-300 Recipients and then 400-500 Recipients, lets see how it goes.