Disposable email addresses
Yahoo! Mail does a terrible job filtering spam. They take email from family members in my address book and put them in the spam folder. They also don't allow you to search the spam filter, and they don't disallow emails with future 'sent' dates.
One decent thing Yahoo! mail does allow you to do is to set up disposable email addresses. These are like those one time use credit card numbers. The good thing is you can block the email once it get compromised. The downside is it breaks many things such as opting out of normal mailing lists. Gnu's mailman will ask you to send an email, and your send from address won't be the disposable one. However, when you do get spam sent to the disposable address, it gives you a really good feeling. Today I was searching through my spam folder, and found this email: