Core PHP Programming, Third Edition

24.6. Verifying an Email Address

It doesn't take much experience with email to discover what happens when it is misaddressed. The email is returned to you. This is called bounced email. Consider for a moment a Web site that allows users to fill out a form that includes an email address and sends a thank-you message. Certainly, many people will either mistakenly mistype their addresses or purposely give a bad address. You can check the form of the address, of course, but a well-formed address can fail to match to a real mail box. When this happens, the mail bounces back to the user who sent the mail. Unfortunately, this is probably the Web server itself.

Reading through the bounced email can be interesting. Those running an e-commerce site may ...