The following dangerous and naive misinformation was posted on the Facebook page of Peppertree Press, and on the blog of Peppertree boss Julie Ann Howell: "I often get questions from authors about copyright. My favorite way to copyright might sound old fashioned; however... it works. Print out your manuscript and then mail it to yourself and do not open it. Tuck it away in a drawer. It will stand up in a court of law."
It probably won't stand up in an American Court.
The practice of mailing a copy of your own work to yourself is sometimes called a “poor man’s copyright.” This is not a substitute for official registration and it probably won’t be useful in a lawsuit. It is easily faked by mailing an empty envelope and inserting a document -- even years later.
There is no way to prove when the envelope was sealed.
A publisher should know better. If you book is published by Peppertree, make sure they use the standard method of copyright registration, not Julie Ann's "favorite way."
An ignorant fool even provides visual instructions for achieving non-protection on YouTube.