StefanNET

Use eval() only if you are sure there is no other solution, and only if you are 200% sure your data is safe.

If e-mail is not delivered, that is up to your hosting (I assume you use mail() function). To avoid this, use SMTP, there are plenty "free" services which offer this feature.

Isn't mysql_* long time deprecated? Use PDO or mysqli instead.

If you are doing some examples. and explaining some of your code, or want to make tutorial, sure you can use CREATE TABLE IF NOT EXISTS .. But you should really create db structure manually.

Is it really going to registration page? I see you have <form action='' with should be <form action='registration.php' if you are using submit form for registration.

If I understood you well, you are looking for this function: http://php.net/manual/en/function.htmlentities.php with htmlentities your code wont be executed as php.