I’ve always wondered if this were possible, after all an e-mail address doesn’t have an IP which you could ping and see if it actually did exist. But surprisingly, one can indeed validate an address without sending an e-mail to it.
The Lifehacker blog has a post about a service that connects to the respective e-mail server and checks if the user, format, and domain that form the e-mail address you specify do actually exist. I concocted five fake e-mail addresses and checked their validity using this service. The service was spot on and gave a “bad Request” message for each. This just might come in handy so worth including in < my del.icio.us account. (via Lifehacker)