The Royal Mail postmark, which will be applied to all stamped post between April 26 and May 1, reads: "Happy 100th Birthday Captain Thomas Moore NHS fundraising hero 30th April 2020."
The Second World War veteran, originally from Keighley, has raised more than £28 million for the NHS by walking laps of his garden in Bedfordshire ahead of his milestone birthday.
His original target of £1,000 was broken in around 24 hours and he extended his challenge to 200 laps after he completed the first 100 14 days ahead of schedule.
Join our new coronavirus Facebook group for the latest confirmed news and advice as soon as we get it www.facebook.com/groups/yorkshirecoronavirusThe postal recognition comes after Royal Mail had to adapt its sorting machines in the South Midlands Mail Centre to re-route all post to Captain Tom into a dedicated collection box.
A spokesman said staff had already processed more than 100,000 cards using this new process and were expecting thousands more in the run-up to his birthday.
David Gold, director of public affairs and policy at Royal Mail, said: "What Captain Thomas Moore has achieved is truly phenomenal, and this is reflected in the affection shown for him across the world.
"As Royal Mail works to keep the country connected during these challenging times, we are honoured to issue a special postmark in celebration of his 100th birthday.
"We continued to deliver the many tens of thousands of birthday cards from well-wishers across the UK and abroad as people look to show their gratitude for all he has achieved on a more personal level.
"We would like to extend our own best wishes and congratulations to him from everyone at Royal Mail."
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