The Labour leader made the pledge as he supported posties in North London marking National Postal Workers’ day.
He warned that privatisation threatened workers’ pay and conditions as well as the universal service obligation that guarantees everyone in the UK gets their post delivered for the same price.
“I want to see a publicly-run Royal Mail, with protection for workers and the service.
"Labour will be doing our very best to support and protect your conditions,” he told workers outside the Mount Pleasant sorting office.
Mr Corbyn said ending the universal obligation could see rural communities “end up with no postal service whatsoever.”
Jeremy Corbyn shows support for posties on National Postal Workers' day
The CWU is using National Postal Workers’ day - the busiest day of the year for the service - to highlight the threat posed to Royal Mail from the Government’s sell off.
The union fears that a review by the regulator next year could result in a two-tier workforce, with new staff on worse pay and conditions.
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.
All mail line up: Jeremy Corbyn addresses posties outside a London sorting office
“Royal Mail may have been sold off on the cheap, but the service is and always will be the people’s post.”
Writing for Mirror online , Mr Ward urges supporters to back the CWU’s People’s Post campaign .
He warns the regulator, Ofcom, “seems determined to support companies who cherry pick the most profitable parts of the business, rather than stand up for a nationwide service.”
