Messages from its free e-mail service will include a "domain key", a system that creates a digital signature for outgoing e-mail and then lets receivers verify that the message comes from where it claims. The technology tries to thwart spam "phishing" attacks where messages pretend to originate from a familiar address and then launch viruses or social engineering hacks when opened.
The changes won't be noticeable to the Yahoo Mail user, since domain keys are resolved in Yahoo's servers and network infrastructure.
Brad Garlinghouse, vice-president of communications products at Yahoo, said users "simply use Yahoo Mail and get the benefit of knowing that we use DomainKeys to prevent attacks".
While Yahoo has talked up DomainKeys as a powerful weapon against spam, for the system to work, outgoing and incoming e-mail services must use the keys. So far, Yahoo has picked up endorsements from EarthLink and its archrival Google. But the biggest e-mail providers, America Online and Microsoft, remain in the wings.
AOL and Microsoft have said they're looking at DomainKeys, but the providers are pushing their own anti-spam and e-mail authentication technologies. SPF -- used by AOL -- and Microsoft's Sender ID check an e-mail's identity through its internet protocol address, and can be used alongside DomainKeys.
Meanwhile, Yahoo on Monday will introduce yet another storage upgrade to its e-mail service, this time up from the 100MB boost in June to 250MB. Yahoo and Microsoft's Hotmail have made similar moves following Google's entry into the free e-mail business with Gmail, which launched with 1GB of free storage.
Until that point, Yahoo and Hotmail offered 4MB and 2MB of free storage, respectively, and charged fees for people requesting extra space.
In addition, Yahoo will increase the attachment limit for its premium subscribers to 20MB, while free e-mail users will continue to get 10MB.
