I don't know how many newbies have figured this out, so here goes: The default for IM's is to save a copy of all sent items in your sent folder. These were not obvious to me when my IM box was full and refusing new messages. To delete all of them the unlabelled white box in the upper right side checks all the boxes to make it easier to delete. Of course this may be subject to the theme you use to view the site it, and I use the Apple one. The buttons are easier for me to read in the apple mode.