Version: 1.11.3 (using KDE 4.2.3) OS: Linux Installed from: Slackware Packages In KMail's composer window, when you attach something there is a list of the attached files on the bottom of the window. This list has columns like "Name" "Size" "Encoding" etc... The "Type" column can not be resized.
From the code I see that this was done intentionally so that the list always uses the full width of the window and the Type column is stretched to use the most space.