According to the documentation and the configuration GUI of the NList.mcc class (which is used in YAM for displaying the mail list) one should be able to select multiple entries in a Listview by using the CTRL+Up/Down keys. However, when I use these keys the listview scrolls to the beginning or end rather than allowing to select multiple entries.

The reason for this problem is, that the default keybindings of NList.mcc and the default keybindings of MUI itself clash. So when you use CTRL+Up/Down the default MUI keybindings will have preference over the NList settings and thus won't trigger the correct functions in NList itself.

The solution is to either upgrade to NList release 0.108 or later as the default keybinding have been changed to use ALT+Up/Down rather than CTRL. Just make sure that you reset the keybinding settings in the MUI configuration pane of the NList classes after you have installed 0.108+ of the NList classes. Another solution (for older NList versions) would be to manually change the keybinding settings in the MUI configuration to use the ALT key rather than CTRL key (see all the "Select XXX" entries in the example screenshot below).