Deleting PMs

[Amber]

Hi, quick question for the programmer. I have rather neglected my in and sent boxes for pms and now have pages and pages of them so would like to be able to delete all but the most recent. Is there a way of selecting all of them and then just unchecking those I want to keep? The system allows me to re-sort by date but only for the page I am actually deleting, then it reverts to the default order, and it is quite cumbersome to go through each individual page reordering, checking, deleting, confirming. Just wondering...