Yahoo! Mail features a number of security measures that increase your email safety.

• SpamGuard technology combats spam
• Phishing message detection helps prevent messages containing known phishing sites from reaching you
• Virus scanning and cleaning from Norton AntiVirus helps keep your computer from being infected with known viruses
• HTML image blocking saves you the hassle of viewing images you don't want to see, and helps prevent spammers from knowing you opened their email
• SSL-encrypted login -- If your browser supports it, your username and password are protected via industry-standard Secure Socket Layer (SSL) encryption when you sign in
• DomainKeys indicator shows if a message is really from a domain, which further protects you from spam