SAN FRANCISCO — Chalk up another casualty of the digital revolution: the blue corner mailbox.

Because of steeply declining use, the U.S. Postal Service has removed more than 60 percent of the blue boxes, once as common on the American streetscape as lampposts and ice cream trucks.

“No

thing says you’re on an American street more than the blue mailbox,” said Nancy Pope, postal historian at the Smithsonian Institution in Washington, D.C. “It’s part of a neighborhood identity, it’s reassurance, it represents our ability to communicate with one another. When you take this away, something is lost.”

In 1985, nearly 400,000 blue mailboxes graced American streets. Now only 160,000 remain, and more are vanishing every day.

The chief culprit is the Internet. More people are paying bills, sending invitations and writing personal letters online. The volume of mail dropped into mailboxes has dropped 35 percent since 2006, said Sue Brennan, a U.S. Postal Service spokeswoman.

If a mailbox gets fewer than 25 pieces of mail per day over a six-to-eight-week period, it gets targeted for removal. The Postal Service posts a 30-day warning notice on the box, during which time people can complain to the postmaster. Then it’s off to the great dead-letter office in the sky.

“To be honest, we don’t get a lot of complaints,” said James Wigdel, a spokesman for the U.S. Postal Service. “The younger generation is moving everything online.”

The defunct mailboxes are stored for spare parts or sent to the scrap heap.

Before mailboxes were introduced in the 1850s, people dropped off mail at a post office — miles away, in most cases. Or, they had to wait for the mailman to come to their homes, not always a reliable event.

Mailboxes allowed people to drop off mail 24 hours a day. The pickup times coordinated with local train schedules, so people knew exactly when their letter would be shipped and had a decent idea when it would arrive.

In a rapidly expanding country, this was revolutionary, Pope said. Speedy communication was good for commerce, journalism and personal relationships, and was an overall boon for democracy, Pope said.

“The ability to communicate with each other, it’s in our Constitution,” she said, referring to the First Amendment. “If people don’t know what’s going on, they can’t make informed decisions. The Postal Service — including mailboxes — helped make all that possible.”