Captain Tom Moore, 99, raised more the £27m by completing 100 laps of his garden before his 100th birthday.
The South Midlands Mail Centre has dealt with 25,000 cards, but that number could rise ahead of Capt Tom's birthday on 30 April.
Centre manager Stephen James said: "None of the team have ever known one person receive so much mail."
With the aid of a walking frame, Capt Tom completed 100 laps of the 25m (82ft) loop in his garden in Marston Moretaine, Bedfordshire, in 10-lap sessions.
