Visiting a sorting office in Mount Pleasant, central London, the casually dressed Corbyn blended in with postal workers as he pledged his support for a campaign to preserve the universal service of deliveries to all 29 million homes and businesses in the UK.
Looking more like worker than the leader of Her Majesty's Official Opposition, the tieless Corbyn posed for selfies and even found time to sort through the mail.
The veteran MP went on to evoke the children's character Postman Pat as part of his plea to preserve part of the "fabric of our society".
Corbyn said: “Since privatisation, Royal Mail has a different ethos.
"I’m concerned that with regulation coming to Parliament next year the universal service is under threat."
He spoke of the problem of developing a two-tier workforce between those recruited prior to the sale of Royal Mail and those hired under its private ownership.
"It’s not just a delivery worker going down the street every day. They are part and parcel of the very fabric of our society, of our very community being.
"Every child growing up learns about Postman Pat, every child growing up sees the postal delivery person as a friendly face that’s going to give them something nice.
"Or not so nice, they deliver bills as well."
Corbyn told workers gathered in the car park of the huge Mount Pleasant site that he will organise an Opposition Day debate in the Commons next year to support the Communication Workers Union (CWU) campaign.
"I want to see a publicly-run Royal Mail, with protection for workers and the service," he said. "Labour will be doing our very best to support and protect your conditions."
Corbyn also called on Conservative MPs to support the campaign, warning that services to rural areas would be among those under threat by any changes such as increased competition, with other companies taking over the so-called "final mile" deliveries to houses.
The CWU designated today National Postal Workers Day as part of its People's Post campaign.
General secretary Dave Ward said: "National Postal Workers Day - traditionally the busiest posting day of the year - is your chance to give posties across the UK the recognition they deserve.
"The CWU is campaigning hard to protect the terms and conditions of our members at the same time as preserving the service that we provide to the public and businesses.
"Royal Mail may have been sold off on the cheap, but the service is and always will be the people's post."