Hi, do you mean the welcome email or a newsletter sent to three lists? A newsletter addressed to three list is sent only one time if a subscriber is connected to all the lists (the subscriber is unique).
What I meant is that there is a post in three categories A, B and C each.
These posts are sent to lists A B C .. will user receive three emails, each for each category, or will script merged three posts from A B and C and send only one email?