Avant Card, Australia's first postcard advertising company, will close its doors this week.

Seen in stands in cafes, universities and art galleries, its unique and bright free postcards have supported galleries, musicians, films and many charities over its 25 years.

Founder and managing director Pat Mackle said digital advertising and social media, as well as a funding cut to the arts, were behind the company's closure.

Avant postcard stands have been a common sight in cafes. ( Facebook: Avant Card )

"It's been really hard ... digital media really affected the business with many clients putting their budgets into digital," she said.

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"When you walk into a cafe now everyone is on their phones, whereas 25 years ago people were posting the postcards and going crazy for them."

Ms Mackle first saw the concept while travelling in Copenhagen and thought it would work in Australia.

On her return she started the company from her home in 1992.

"I was uncertain in the beginning if it would take off, but I knew there were other people who appreciated arts and culture like me," she said.

The company has created more than 20,000 campaigns and distributed more than 250 million postcards.

"It's nearly five postcards for every Australian and there's not too many people I meet in my travels who don't know of the free postcards," Ms Mackle said.

The most popular postcards

Ms Mackle said she had many favourite cards over the years.

"There was one of Norman Gunston giving the bird and another of Mr Bean in his underwear.

"Recently we did a series of cards for the Lego movies and we designed them in-house ... they turned like a spinning wheel, which was cool."

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Ms Mackle recently posted a farewell letter to her beloved postcards on Instagram:

Dear Avant Card, Thanks so much for being my best friend, for giving me a great life, for introducing me to so many amazing people, for allowing me the privilege of giving back to society and for being part of so many people's lives. I have loved every moment. Yours sincerely, Pat Mackle

She said since the closure announcement, the company had been inundated with messages from fans devastated that the postcards would be no more.

One letter she received was from an aunt who sent the postcards to her nephew every week; he had been fighting an ice addiction.

"She wrote to me and told me he had broken his addiction and now his room is plastered in our free postcards," Ms Mackle said.

An image from the Art Gallery of New South Wales was a popular postcard. ( Facebook: Avant Card )

"I really hope the cards brought happiness to others too — when people collect something they love it and it becomes a keepsake.

"We had the motto, 'the best things in life are free', and that's what we stood by."

Saying goodbye with Elvis

The final card issued was number 20,850 titled "Elvis has left the building".

"People would go to Elvis concerts and no-one would leave, so I think that's the sentiment," Ms Mackle said.

"The imagery of him dancing and holding the postcard with the final farewell message seemed so right."

She said the company was in talks with the National Library in Canberra to house the entire collection of postcards, and in Queensland Creative Brisbane would be taking over the postcard stands.