Roberia Lima dos Santos steps timidly up to the counter and asks in a tiny voice if this is the place where they write letters.
"I want to wish my son a merry Christmas and tell him I won't be able to visit him in prison," says the functionally illiterate Brazilian woman.
Dos Santos, a 64-year-old cook, is one of thousands of Brazilians who have turned to this free service provided by the Sao Paulo state government since 2001 to write letters on behalf of those who cannot write their own.
"Tell him I send him kisses, to go with God and that his sisters are all well," she tells one of the volunteers who work on the program.
Her 38-year-old son is in jail for robbing banks. She isn't able to visit him this Christmas, but wants him to know she is thinking of him.
She tells AFP she does know how to write a little, but sought out the program to make it easier.
When the volunteer asks if she wants to sign the letter, she takes the pen and slowly writes her name in big, round letters.
Fourteen million Brazilian adults are illiterate, according to UNESCO — seven percent of the sprawling South American country's population.
It has the eighth-highest number of illiterate citizens in the world.
Millions more — another 17.8 percent of the population — are functionally illiterate. They know their letters and numbers but cannot fully read and write.
"I'm always surprised by the number of people who don't know how to read and write, or who know how but can't express themselves properly in writing," said Vera Rocha, who has been volunteering with the program for the past two years.
A 71-year-old retired teacher, she loves her volunteer work, she says.
"Sometimes people come and say, 'Tell them I miss them and I love them.' But you can't fill a whole letter with that. So we ask them why they are nostalgic, who they miss, why they don't see this person anymore, if there was a falling-out," she told AFP.
And that becomes a full letter, she said.
The program is reminiscent of the acclaimed Brazilian film "Central Station," in which a cynical retired schoolteacher who writes letters for illiterate clients is befriended by a little boy who needs her help to find the father he has never met.
The volunteers have written love letters, hate mail, letters to long-lost relatives, letters "seeking someone to listen," said Rocha.
In the working-class neighborhood of Itaquera, the program has sent 42,000 letters since 2009.
Most are addressed to TV programs, though many are also sent to prisons.
Many people ask for help paying for medical treatment or home improvement projects.
Valeria Correia, 29, was asking for money to pay for an operation she needed.
"I don't know how to say what I want to say, that's why I came here," she said.
Besides writing letters, the volunteers help fill out forms, request official documents and file complaints.
At this time of year, there is also a special mailbox for Santa Claus.
"The truth is, people are writing less and less letters," said program coordinator Zulene Chagas.
"With the Internet and Facebook, everything has changed so much."
Most people who use the program are over 50 years old.
In the movie "Central Station," which was nominated for best foreign film at the 1999 Academy Awards, the professional letter-writer sometimes never sent the letters she wrote for desperate clients at her impromptu stand at Rio de Janeiro's main train station.
Rocha guaranteed that was not the case with her program.
"We do send the letters — we're not like her!" she laughed.