I hope, you don't try to open e-mails in PowerPoint, but only the
attachments. Are these presentations containing photos? Are only the images
upside down or text, too? Are you using PowerPoint or only PowerPoint
Viewer? Which version? Do you know which version the presentations were
created in? There was an issue with images inserted in PowerPoint 2000 which
appeared flipped in 2002/2003. This cannot be corrected in the Viewer, for
the full version of PowerPoint there's a correcting Add-In: http://skp.mvps.org/unflip.htm.