we sent a power point show(.PPS/.PPSX) via email. The issue is, recipient (uses MS office 2010) cannot open the file as a power point show. it always open in protected mode just as a ppt/pptx opens. But when same slide show sent from web-mail (outside our org) this open as a slide show, which we desire. Other strange thing is that users which has MS Office 2007 have no issue opening this attachment as a slideshow.
we are using MS Exchange 2010 as our mail system.