How do I filter a ListSouce list?

[Norm Bessette]

been buying multi family units for buy and hold on MLS for the past few years and built to 50 rentals but now looking to expand and considering ListSource. My question is what have people used to filter the database you receive and simplify the production of letters and/or postcards? Looking to see how people have automated or semi automated it.

Also interested in feedback on best approach- letters or postcards and is there a way to save on bulk postage