"We've teamed up with eBay and PayPal to become the first Web mail service to block the delivery of unauthenticated eBay and PayPal emails, reducing your risks of receiving phishing scams or fraudulent emails. Our weapon is a technology Yahoo! spearheaded called DomainKeys, which uses cryptography to verify the domain of the sender."This is the first major announcement of this kind, be prepared for more to follow by authenticating your mail now. Not just your commercial or transactional email but also your Corporate email.