Instead of the more traditional “Happy Birthday” song, the National Postal Museum will celebrate its 10th anniversary today to the more applicable tunes of “Return to Sender” and “P.S. I Love You,” among others.

Underneath three vintage airplanes hanging from the 90-foot ceiling and amid a reconstructed railway mail car and an 1851 stagecoach, the a cappella group Passing Notes will perform postal-themed songs at the museum’s birthday bash — in costume. The coed group will sport real postal uniforms for the celebration, which kicks off at noon and wraps up at 4 p.m.

The 15,000-plus visitors expected to attend the event, located in the Old City Post Office Building adjacent to Union Station, will also be able to watch a dramatic interpretation of the first female postmaster, take tours of the museum’s stamp collection and postal history collection, see a printing press in action, test pens ranging from quill to gel and make their own birthday cards.

“We are celebrating the core of the museum,” said Kim McCray, the museum’s public programs coordinator, who estimated that the museum gets an average of 400 visitors a day.

Boasting more than 3 million visitors since the Smithsonian Postal Museum branched off from what is now the National Museum of American History in 1993, staff and visitors alike said they are surprised and pleased by its success.

“I didn’t think people would want to come here,” said Ramon Alvarado, a Postal Service employee from Kissimmee, Fla. As he watched several families descend the escalators into the museum’s atrium, he said he thought, “Wow, there’s a lot of people here.”

The museum was an important stop on Alvarado’s vacation agenda because of his close ties to the Postal Service. He added that the exhibits are “awesome” and he “liked it better than the Natural History Museum.”

The national stamp collection was established at the Smithsonian in 1886 with the donation of a sheet of 10-cent Confederate postage stamps.

“It’s like going back in time,” said museum visitor and Woodbridge, Va., resident Joseph Bassarab. “I don’t think the younger generation really appreciates the service they gave.”

Bassarab, a Washington-area resident for more than 30 years, added that he remembers when the space the museum now occupies was “the place where you could drop off your income taxes.”

On its 10th birthday, McCray said the free celebration will honor the “people who have made this place possible” and the “stories the museum tells.”

The Postal Service history provides a unique insight into the way transportation and communication developed in America because they are so closely related, McCray said.

“Many different types of vehicles in transportation history were used as a form of mail delivery,” she said, sighting hot air balloons and hovercrafts as proof.

Around 35 volunteers will assist the museum’s 20 staff members with the birthday party, including the 80-year-old Miles Manchester, who has been a museum volunteer since it opened.

Looking forward to another 10 years of service, David Umansky, the museum’s associate director, said, “We’re very optimistic about [the future].”

In October, the museum will open an exhibit on heroic deeds in the Postal Service, which will range from the stagecoach days to Sept. 11, 2001, to recent anthrax scares. For this collection, the museum has already obtained a battered blue mailbox that survived the Sept. 11 attacks at its location directly in front of the World Trade Center. It now resides next to a rolling mailbag that was used in the halls of the buildings.

In April 2004, the museum will receive a portion of Queen Elizabeth’s personal stamp collection. Museum representatives met with the “keeper of the royal philatelic [or stamp] collection,” Umansky said, and “he was pleased and agreed to ask Queen Elizabeth.”

With the royal thumbs up, the museum will feature the largest-ever presentation of the Queen’s stamp collection and will include copies of the first stamps ever used in England.

“It’s a big deal,” Umansky said. “We have been working on this for almost a year. It’s something that will draw philatelists from all over the world.”