After scrapping Jersey's daily mail plane last August, Royal Mail says it will withdraw funding of Guernsey's service in April 2025.
Deliveries now come to Jersey by ferry, meaning a two-day service for post to and from the UK.
When the Royal Mail scrapped the daily flights last August, it said Guernsey's would stay in place.
This was influenced by the heavy use of the service by the Guernsey-based online greetings card giants Moonpig and Funky Pigeon.
But Royal Mail has told Guernsey Post it has to save money and will withdraw its 50% funding of the aircraft in April 2025.
Guernsey Post CEO Boley Smillie says they have known about this for some time:
“We were informed of Royal Mail’s change in position earlier this year, which was disappointing news.
"However, we have been working hard to secure a deal with alternative potential partners.
"As commercial negotiations are underway it is too early to comment further but we are making good progress. Our priority is to secure the current or a similar aircraft and maintain next day delivery services to the UK from Guernsey.”
A spokesperson for major clients Moonpig said:
"We are doing everything we can to find an alternative arrangement following Royal Mail's recent announcement and have been working closely with Guernsey Post to find a solution that will enable the continuation of this service."
Volumes of traditional letters have been decreasing year on year as people and businesses communicate electronically.

Commonwealth Games: Nowacki into 100m breaststroke final
Channel Islands face 'physical' Poland test
Thousands expected at Havre Des Pas Festival this weekend
Price of heating oil and other fuel increase by more than half in a year
Man jailed for importing nearly £600k worth of cannabis in bumpers of his car
Baby born on Guernsey's Marine Ambulance
Drug trafficker who claimed he was the ‘Accredited Dealer' jailed
Jersey men involved in cocaine importation sentenced