A simple way is to upload it somewhere where it's only viewable with a restricted Flash viewer to prevent copy/paste, then delete it once it expires. Of course,

A simple way is to upload it somewhere where it's only viewable with a restricted Flash viewer to prevent copy/paste, then delete it once it expires. Of course, the person can always take a screenshot or photograph the monitor or something like that. Most temporally-limited email services do not deliver the message itself, but a link to it.