I always think twice or even three times before I enter my e-mail address in a Web form. Even when the site gives me the option not to have any messages sent to the address (usually by unchecking the Web form's "Notify me" entry that's checked by default), I can't help but think somehow, somewhere, some snake-oil salesman is going to get hold of my address.
Now I register at such sites using a separate e-mail account whose mail I filter out of my in-box. When I have to click a link in a confirmation e-mail to complete the registration, I simply look for the message in the folder I specified previously.
Start by creating a POP or IMAP account only for Web site registrations. Most ISPs offer multiple mail accounts for free. In fact, when I last checked, I had 114 free mail accounts available with my ISP. Of course, I've also registered five different domain names with that company, each of which comes with several mail accounts.(Maybe I could sublease the ones I'm not using.)
If your ISP doesn't offer multiple e-mail accounts, sign up for a free account at a service such as Inbox.com. The company offers up to 5GB of mail storage for free and allows POP3 and SMTP access to your in-box.
Now add that account to your mail client. In Outlook 2007 and 2003, click Tools > Account Settings > New, choose "Microsoft Exchange, POP3, IMAP, or HTTP," and click Next. Add your account information on the next screen and click Next. Outlook will connect to the server automatically and send a test message.
Once the account is in place, return to the Account Settings dialog box, select the account, and click the Change Folder button at the bottom of the window. Choose one of the existing folders, click New Folder, give the folder a name, click OK twice, and then Close.
Since I forward the mail sent to my ISP accounts to my Gmail in-box, I also need to keep messages sent to the throwaway account from cluttering that in-box. To add the account to Gmail, click Settings in the top-right corner, choose Forwarding and POP/IMAP, and select either Enable POP or Enable IMAP, whichever is appropriate for your account.
Now click the Accounts tab and choose "Add another mail account" in the "Get mail from other accounts" section. Enter the e-mail address and click Next Step. Add your password, check both "Label incoming messages" (the address is the default name for the label) and "Archive incoming messages (Skip the Inbox)," and click Add Account.
After the account is confirmed, you'll be asked whether you want to make this account a custom From address. This allows you to send mail from Gmail and make it appear to originate from that account. Click Yes if this sounds like something you might want to do.
When you need to access a confirmation e-mail sent to your throwaway address, just choose the label in the list at the bottom left of the Gmail in-box and select the message in the resulting window.