Version: 1.13.0 (using 4.4.63 (KDE 4.4.63 (KDE 4.5 >= 20100209)), Exherbo) Compiler: x86_64-pc-linux-gnu-gcc OS: Linux (x86_64) release 2.6.31.6 There used to be a button that will trigger a sort function, but I can't seem to be able to find it now. It was useful.
It is in the View->Message List->Sorting menu. Depending on your message list theme, you have a date header, and you can just click on it to change sorting.