After receiving an “undeliverable” holiday card back, Adam and Tonya Engst discovered that their approach to extracting data from Contacts to print labels inadvertently deleted leading zeroes in ZIP codes. Can they ever send snail mail to New England? Here’s what happened—and how to avoid similar errors.

It turns out that Contacts on the Mac stores extra invisible characters with every phone number, which can cause trouble when copying and pasting them into some online forms. Here’s what’s going on and how to work around the problem.