With Caller ID, you are able to determine the identity of your caller before answering the phone.  Wouldn't it be nice to have this same luxury with e-mail? Especially given all the SPAM we receive these days.  Now, AddressGuard, a new feature from Yahoo! Mail, lets e-mail users better understand why people are contacting them.  Miles Libbey from Yahoo! Mail:

"AddressGuard is similar to Caller ID for e-mail - only better.  You don't just know who is emailing you; you also know why the sender is contacting you.  With AddressGuard, e-mail users create substitute email addresses for different situations like dating or shopping, while protecting their primary address from spam.  If at any point the address is sold or harvested by spammers, the address can be easily deleted, while the primary address is kept spam-free."

Yahoo! Mail's AddressGuard gives e-mail users greater power in the battle against SPAM.