The United States Postal Service (USPS) neither requires, nor checks, to see if an envelope is sealed before it is mailed. Because envelopes can be tampered with and documents can be exchanged, “self-sealed mailings” should not be relied on as solid legal evidence of your copyrights to any form of expression.
The USPS does not condone, and clearly warns consumers not to use registered or certified, self-addressed mail as proof of ownership. If you have something really important to you, of potential or significant value, it is well worth the time and money to protect your interests through formal copyright registration.
There are online resources that you can upload digital images of material to in order to show proof of the creation date. You are then sent email verification with a return copy of your digital image. One free resource to try is MyFreeCopyright.com.
Copyright Tip: Only formal registration can offer you certain legal remedies. If you have not registered a copyright, you cannot even sue someone for copyright infringement in the United States. And, if you did not register your copyright in a timely manner (90 days or less) your right to recover damages in court will be severely limited.