The Problem
I was recently doing some housekeeping on my websever: removing archived software downloads that I no longer needed and looking for any problems when I found one that initially had me stumped. Looking at the size of my home directory, I found it was around 600mb with no immediately obvious reason as to why.
I have hardly any files in my home directory, so I quickly located the problem to ~/Mailbox/.Sent/cur, which is, as the path suggests, related to my email server. It looked like copies of my sent mail was being stored and not deleted.