I use a Mac and I have come across something called 'disk permissions'. What is this? Samantha, Mid-Levels DQ: Disk permissions are intimately connected to software packages installed in a computer, including the most important of all: the operating system. Packages on the Mac end in .pkg and each time one is installed a 'Bill of Materials' file is put in the Library/Receipts folder. These files, which end in .bom, contain lists of all the files needed to install a package and the permissions needed for each file. When Disk Utility is used to repair your machine's disk drive, it opens the .bom files and looks to see if the permissions are all correct. (Launching Disk Utility and telling it to check permissions will show you just how often these things need fixing.) Disk Utility will also repair them if you tell it to do so. Most of the time you'd be better off simply leaving these files alone. If Disk Utility tells you that disk permissions need repairing, you should do it then leave it. Apple says you should not repair permissions if you have started your computer on a DVD-Rom or other disk. Always repair after starting the machine on your main hard disk. Also, make sure all updates have been downloaded and installed. For more information, see support.apple.com/kb/HT1452. I find Google's Gmail filing system, where all messages for each e-mail subject are stacked together, most annoying. Is there a way to reformat this, so I can remove unwanted correspondence and retain only relevant ones? Mary Melville, Kowloon DQ: Gmail uses a system called 'Labels' so you can organise mail in ways that get around the folder problem. The standard way of dealing with e-mail is to put messages into folders you create. Normally, if one creates a folder for Bob and another for Jane, for example, all e-mails from (and possibly to) Bob are put into his folder; the same for Jane. There are times, however, when Bob and Jane may be working on a project with Mary. If the project is Babylon08 then you could create a label of that name. With Gmail, you can give the same message multiple labels. A message from Bob that has the label 'Bob' will be associated with him and if you click on his label you will only see messages from him. But if you click on the label 'Babylon08', you will see messages from Bob and everybody else involved in that project. The Gmail system is extremely flexible, so by judicious labelling, you could organise your e-mail the way you want to. For more details, visit Google Label help (mail.google.com/support/bin/answer.py?hl=en&answer=6560).