They can't track your email address...
As far as the PO Box thing - most of my family has a PO Box, how come a PO box makes something a scam?
I checked Snopes also... here's the direct link to the story (and some background on the story):
http://www.snopes.com/inboxer/medical/bernier.asp
I'll send a birthday card (or 4 or 5 of them) out tomorrow!!