Nope.
[
www.snopes.com]
I doubt this would win a lawsuit for you anyway. For instance, I send myself a letter with a blank page. Later, I steam open the envelope (or put it in the freezer and then open it when the glue is frozen), and put in whatever I want. I re-seal the envelope and claim it was always intact.
Gotta register it if you want protection from the courts.
[
www.copyright.gov]
Not that it much matters for our ilk in any case - consider yourself talented indeed if someone tries to steal your work. If you can create great stuff once, you can do it again (and again). Realistically speaking, it ain't gonna happen for most of us!