Claim: The “Poor Man’s Copyright” is established when you mail yourself a copy of your own work.
If you’ve written a story, song, or play; or painted a picture, taken a photograph, or sculpted a figurine; or otherwise created any tangible creative work, you have established a copyright. Although registration of your copyright gives you some additional options in a lawsuit to enforce it, your legal rights to your work attach immediately once you have created it. Mailing yourself a copy of your work does not enhance your copyright protection in any way.
Additionally, postmark dates are insufficient in court to prove the date of a work’s creation. The post office does not certify that an envelope was sealed before mailing, and it is easy to swap something into a mailed package, so the value of the evidence is low. The only surefire way to establish a date of creation is to register your copyright. If the copyright is unregistered, the burden of proof is on you to show the creation date with evidence like eyewitness testimony from people who saw your work or time-stamped e-mails containing snippets of it.
Since registration is inexpensive and dramatically increases the value of a copyright infringement suit, most attorneys would recommend spending the small fee and the bit of time on paperwork for any work you feel necessary to protect.