>> You would simply have to prove via the posted date that you copyrighted the song

Yes, if you emailed it to yourself at a hosted email like gmail or hotmail, that would be be strong proof of the date that it was sent. Because that couldn't be faked. You could open up the account, and show whoever was interested that gmail or hotmail received the email.

There could be problems with things mailed to your house, because you could mail yourself an unsealed envelope, and then seal it years later, after inserting something after-the-fact.

Have Fun!
Peter Gannon
PG Music Inc.