In article ,
The Natural Philosopher wrote:
An elderly friend is going abroad over Christmas for 5 weeks to visit
family, and wants to know what to do about his letterbox, which wont
hold 5 weeks of mail and would rather give the game away if left stuffed
with weeks old letters.

Poste Restante seems to only hold mail for two weeks.

What are the alternatives?

It's called "Keepsafe". The local sorting office will hold mail until you
return. Collect form at any Post Office or look at Royal Mail's website

--
from KT24 in Surrey, England