Indeed that was my first impression when I saw the example e-mail address "[email protected]", which is a very valid e-mail address according to the RFC. Practically though, you can't send an e-mail to that address, unless your DNS server happens to know where "dottiness" is located, which means it's not a *useful* e-mail address in most circumstances.

Indeed filter_var( ) does tell you some valid e-mail addresses aren't valid, but in day-to-day use in a webapplication, it will suffice easily.