Pro PHP Security: From Application Security Principles to the Implementation of XSS Defenses, Second Edition

When a Working Mailbox Isn't Enough

Unfortunately, a working email address is no great proof of identity, either. At best you have proven that a communication channel existed at one time, and that someone picked up a message at that mailbox. But the barrier for creating a new email address is extremely low. Anyone who owns a domain has an essentially unlimited number of mailboxes at his disposal, and anyone who can solve a captcha (discussed in Chapter 9) can obtain a webmail account at one of the big online email services. So possessing a working mailbox doesn't necessarily mean that much. Over time users will often change their email addresses, either because they are trying to stay ahead of spammers or because they switch jobs or group affiliations. ...