The Letterbox Project founder Mea Campbell said she was thrilled to announce the second-largest manufacturer of tea in the world as the 2021 major naming rights partner.

Ms Campbell is concerned COVID-19 physical distancing restrictions have exposed thousands of people across the country to social isolation, loneliness and vulnerability during the past nine months.

Her idea, which creates connections for people without access or capacity to use technology by sending handwritten letters, has grown exponentially to reach 3.5 million people in the past six months.

Joining forces with Tetley Tea means security and longevity for the project, and will allow for more permanent staff to assist with the team of 47 core volunteers, Ms Campbell says.

"This partnership has enabled us to build strong foundations so that The Letterbox Project can be a sustainable, long-term support system for vulnerable people everywhere," she said.

"We have moved into a private office at The Exchange and are currently interviewing for a local administrative officer role.

"What has been a remote operation with more than 47 volunteers will now be centralised into a safe location with trained staff."

Ms Campbell said Tetley was a household name in Australia, and an organisation "with a longstanding focus on a sustainable environment and the betterment of lives for all individuals".

"Tetley's values and mission aligns perfectly with our Letterbox Project, and I can't think of a better way to connect with others than over a cup of tea," she said.

The partnership had developed after the social enterprise experienced a huge rise in large corporations getting their staff involved in the project, The Letterbox Project founder said.

"Businesses would dedicate time for their staff to volunteer and write letters, and this started growing exponentially towards the end of the year," Ms Campbell said.

"In one week we had Deloitte, Medibank, Sales Force and Twitter AU all participate.

"I saw the potential to find an organisation that aligned with our mission, and one that wanted to support our growth.

"Tetley quickly became the stand-out partner because of their global community impact and their focus for the future... there is so much potential for what we will achieve together in 2021."

The Letterbox Project is one program delivered by Ms Campbell's Connected AU, and she said Tetley's support would also allow room for focusing on growing other programs in 2021.

An Australian Bureau of Statistics' national household impacts of COVID-19 survey showed 28 per cent of women and 16 per cent of men reported feeling lonely as a result of the pandemic.

Tetley Tea brand manager Kleanthis Mantzouranis said the massive growth of The Letterbox Project proved that despite COVID restrictions there was an enormous appetite for social connection that aligned with the company's core values and mission.

"We are so proud to be partnering with a foundation that highlights the importance of reaching out and communicating with others who might be going through a challenging time," he said.

"The Letterbox Project connects those who might be lonely or isolated, and provides them with a conversation and kinship, something we think is so important and pairs perfectly with a cup of tea.

"We can't wait to spread the word about this amazing initiative and see what this partnership between Tetley Australia and The Letterbox Project will bring."