Methods, computer systems, and memory media for preparing instructions for printing a plurality of postage items. A graphical user interface (GUI) receives first user input. Responsive to the user input, an addressee data file is uploaded, features are extracted from a plurality of columns of the addressee data file, and the plurality of columns are associated with respective address field types based on the extracted features. The GUI displays an indication of the association between columns and address field types. User input may modify or correct the association. Responsive to second user input, instructions are prepared for printing entries from the columns of the addressee data file on respective postage items of the plurality of postage items as respective address fields, and the instructions are stored in a non-transitory computer-readable memory medium.