Whenever I give webinars or talks about copyright registration, I continually hear the following myths about copyright registration:
"If I mail my book to myself, that will protect it." False. To protect your work, you don't send it through the mail. You register it with the US Copyright Office.
"My book isn't copyrighted unless I put a copyright notice in it." False. Copyright law no longer requires you to affix a copyright notice to receive protection.
"My book isn't copyrighted if it's not registered." False. The copyright to your work is created once it's fixed in a tangible medium of expression (e.g., saving your book on Microsoft Word). Registration isn't required; however, it provides legal protections.
So what are the legal protections you get from registering your work?
You cannot bring a copyright infringement suit against someone unless you register your copyright.
Registering your copyright provides evidence of the validity of your copyright. Essentially, it's proof that you're the copyright owner.
You are eligible for statutory damages (i.e., up to $30,000 for each work infringed and up to $150,000 for each work infringed if the infringement is willful) and attorney's fees.
So if you think you'd ever sue someone for copyright infringement of your book, you should register your copyright. It's a no brainer. Plus it's cheap and relatively self-explanatory. Of course if you have any questions you can always ask a copyright attorney for advice. Below is a link to the registration portal on the US Copyright Office's website: https://www.copyright.gov/registration/