I have a box full of old letters, mostly from the 1990s — the last decade when people wrote letters. One envelope from 1993 is postmarked “Chicago, IL 606.” You won’t see that anymore, though, thanks to the centralization of mail processing.

In the old days, postal substations canceled their own mail, says Charles Berg, owner of Stamp King in Norwood Park. “As the post office has automated more, they resorted to using more sophisticated machinery,” Berg says. “Small stations can’t operate that way.”

The Chicago postmark disappeared altogether in 2012, when the processing center at 433 West Harrison Street stopped canceling mail and that function was centralized in Carol Stream and Bedford Park. Drop your mail at a North Side station, and it will get canceled as “Carol Stream”; on the South Side, “South Suburban.”

There are exceptions for first-day covers — that is, mail affixed with a new stamp on the day it is made publicly available — and ceremonial mail. I collect first-day covers of famous authors and have a Richard Wright one, issued in 2009, postmarked “Chicago.” When Barack Obama gets his presidential stamp, you can bet that first-day cover will be postmarked in Chicago, not Carol Stream.

Email your questions about the Chicago area to emcclelland@chicagomag.com.