If you change your email address due to an Internet provider switch or other reasons, once the new address is active, send a notice from that mailbox to everyone you regularly communicate with via e-mail. While making the new address your primary one, keep the old address for a month or two. Check both regularly, but send mail exclusively from the new account. If any people send you mail at the old address, be sure to alert them to the change, but send that message from your new address. Once you've gone a week or two without getting a new, pertinent message at the old account, you can cancel it.