Hi. I'm having this problem, and using HMTsu and Filebox I was able to pare /home/user/ .qmt down to 240+ MB from 700+, but I can't delete the rest. Thankfully my mails seem to still be there. Settings/Application usage (and df -h) still report more than 1.5GB used on the Application data partition. Using FolderPie I see that /home/user/.thumbnails is using almost 500MB. Is it safe to delete .thumbnails and how can I do it? Thanks.

[edit: no, in the end, I had to delete all mail accounts, rm -rvf /home/user/.qmf as *regular* user, and then reconfigure my mail accounts. It solved the bug where one of the accounts did not notify of new mails, though ]