Error Checking

Hello Everyone, Could someone suggest the code to me that will check for user input error. Example, I am asking for an email address to process. When the php3 script begins, I need a snip of code to check that the email address is not a house address. The php3 currently returns an error, but it continues on, telling the user the letter is sent to the dead letter box. I want to check to see the input is right, and if not, direct the user to re-enter it. Thanks for any help you can give me.

Dar...

You might the class.Validator.php3 you can get off of http://www.thewebmasters.net/php/