<A target="_blank" href="http://notesbusters.com/2011/01/03/domino-8-5-2-hf1-the-fix-for-the-unread-synch-server-crash/">Victor Toal says, if you have experienced a server crash</A> on Domino 8.5.2 when users sync unread marks, you may want to get Hot Fix 1. HF1 fixes this regression bug.