I was 5:25 p.m., but colleague Bill MacKaye was in a hurry to get a letter to a free-lance writer who lives in Bethesda. Our mail room is supposed to close at 5, but Bill got his letter into the last batch of outgoing mail.

At 2:45 the next afternoon, the free-lancer received Bill's letter and phoned him. He thinks the Swift Couriers of the USPS deserve a pat on the back.

They deserve about 100 billion pats on the back every year, but the incidents we remeber are usually the ones in which somebody goofed.

Incidentally, mention up USPS reminds me that many readers are puzzled when they receive letters that bear only 13 cents in postage. "Is my bank cheating the government?" they ask. Or, "How come the public utilities can send out letters for 13 cents when I have to pay 15 cents?"

The next time you receive a letter like that, notice that 1) it is from a large mailer, 2) it does not carry a stamp but is imprinted with a postage meter, and 3) at the extreme left of the imprint are the words, "Presorted First Class." USPS says that presorting by large mailers saves the Postal Service at least two cents per letter, and that the reduced rate therefore benefits both parties.

For a public utility that sends out 500,000 bills a month, presorting means a postage outlay of $65,000 a month instead of $75,000 a month -- or a saving of $120,000 a year minus whatever it costs to presort.