The United States Postal Service shared some useful holiday mailing tips with us a few weeks ago, with some sensible suggestions to help you get your packages to their destinations faster and with a minimum of fuss. An anonymous postal worker complimented that list, but told us that she had some additions of her own: insights that can only come from behind the counter. 

Don’t mail anything that isn’t a piece of paper in a regular old envelope. Greeting cards, fine. It might seem like you’re saving money by just folding that thumb drive in a handful of sheets of paper and sending it off like a letter, but the mail doesn’t work that way. “The glue is not very strong and anything lumpy or irregular comes right out of them,” our tipster writes. How does she know this? “Every year someone mails a bracelet, necklace, car keys, thumb drive, etc., in an envelope designed for letters.”

Similarly, some items might be small and flat, but that doesn’t mean that they can make it through the postal system’s automated sorting equipment. Like gift cards. “We destroy thousands of dollars of gift cards each year,” writes our tipster. “Gift cards come out of envelopes all the time.” It’s not a vast USPS conspiracy to steal America’s gift cards, and there are two simple ways to avoid having your gift cards gobbled by a letter-sorter.

First: don’t think of it as an upsell when the postal worker tells you your envelope requires an extra non-machinable charge. The extra charge keeps your envelope out of equipment meant only for letters. Extra insurance: put an address sticker on the gift card. “If there is an address on the card, we will send it on to the destination or back to the sender,” our tipster notes.

Listen to your friendly local postal worker. Our tipster might be biased as far as this goes, but she wants our readers to know that she and her colleagues really don’t enjoy wrecking packages. “Trust that most of the people at the post office are professional and really do want to your packages to reach their destinations safely,” she advises. “We are paid very well to do so. When they advise that a box might not survive the shipping process or that a fragile item needs more padding, they mean it.”

Vintage Christmas cards are great and all, but be careful. We wouldn’t have thought of this one: it might be really cool to raid your grandmother’s old box of cards or pick them up at a thrift store, but consider buying a new envelope or sticking the whole thing in a larger envelope and putting the address on that, just to be sure. Why? Old paper and glue. “Paper gets very brittle, and the machines tear them up and destroy old envelopes,” our tipster notes. “then everything, cards, pictures, and gift cards come out of the envelope.”

Plan ahead, just a little. The Christmas stamps will most likely sell out by the week before Christmas. You should have mailed your cards before that anyway. Similarly, while your gift will probably make it across the country in time if you run to the post office on December 21, don’t count on it.

We know that a lot of you have particular insights into jobs and businesses that most consumers don’t know much about — or about which they make huge assumptions. So if you feel like sharing your thoughts on what it’s like to work retail, or food service, or in the shipping, banking, hospitality fields (or something we failed to mention here), feel free to share your insights with us at tips@consumerist.com.

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