Non-machinable surcharges are a significant and often invisible cost driver. Pieces that exceed letter dimensions, weigh too much, or fall outside USPS aspect ratio tolerances trigger surcharges that add several cents per piece. Designing mail to qualify as a standard letter or flat rather than triggering non-standard fees requires attention to USPS mail prep standards upfront, but pays off immediately at scale.
Common pitfalls include envelopes with clasps or strings, rigid enclosures, square formats, and pieces just over the weight threshold. Working with a print-and-mail vendor whose design team understands current USPS specifications means these issues get caught before production rather than after 50,000 pieces are already printed. Across a single campaign, right-sizing is a reliable driver of direct mail cost savings that requires no list changes, no postage class switch, and no additional vendor coordination.