How To Mail Merge Four Postcards Onto One Sheet Step 3: Start The Mail Merge. Before starting the Mail Merge, in this step you would also create your postcard design. In order to keep the focus on Mail Merging for this post, we're going to skip the whole design step and move right on to creating the Mail Merge. In the Main Menu at the top of the window, go to: Tools > Mailings and Catalogs ...