How did Dobby the house-elf intercept Harry's mail during Harry's summer holiday between Philosopher's Stone and Chamber of Secrets?
‘See what it’s like here?’ [Harry] said. ‘See why I’ve got to go back to Hogwarts? It’s the only place I’ve got – well, I think I’ve got friends.’
‘Friends who don’t even write to Harry Potter?’ said Dobby slyly.
‘I expect they’ve just been – hang on,’ said Harry, frowning. ‘How do you know my friends haven’t been writing to me?’
Dobby shuffled his feet. ‘Harry Potter mustn’t be angry with Dobby – Dobby did it for the best...’
‘Have you been stopping my letters?’
‘Dobby has them here, sir,’ said the elf.
Chamber of Secrets - page 19 - UK - chapter 2, Dobby's Warning
I saw a similar topic at another Q&A site while I was looking for a JKR interview link and thought this question might be a good fit for SE. I hadn't thought about it before, but it does seem like tracking Harry's mail would be a full time job that would've pulled Dobby away from his indentured servitude for the Malfoys. How did he manage it?