A neat trick that I discovered at university was that VMS' email system used 'sparse' disk blocks for your personal mailbox file, and immediately after forcing

A neat trick that I discovered at university was that VMS' email system used 'sparse' disk blocks for your personal mailbox file, and immediately after forcing a rebuild of your mailbox by compacting it, you'd have dozens of sparse, uninitialised, disk blocks in your file - which you naturally had read access to. Since compacting mail was the most common activity on a time shared university system, the odds were a good number of those uninit'ed blocks would be other people's erased blocks, and thus you could essentially read other people's emails just by sitting and compacting your email, then hex viewing the raw mailbox file.