Hi,
if you want to always skip them you can in "Settings" -> "Process" -> "Files" -> "Skip posts with main files extensions" -> enter:
Code:
rar,zip
Press "Save" button.
Or, you could add a banned word in "Settings" -> "Words" -> "Banned words".
They are assigned to specific section too. Just add ".rar" (with a dot, since rar might be in some random word). Banned word is checked against full filename (with extension). You can also enable to "Search in subject only" (this will still check against full filename, but won't waste time checking in message text later).
There is option for banned word to delete those files as well if needed.