"Sender ID doesn't have the momentum," said Matt Sargent, senior anti-spam technologist at secure email firm Messagelabs. "It's mostly valid under SPF as far as current specification is concerned. But not publishing their own protocol is a bit strange."
Many industry watchers are concerned about Microsoft owning patents covering a proposed standard for a public authentication system and have balked at using it. Even so, Microsoft pushed SenderID at the recent Email Authentication Summit and companies such as AOL and Paypal use the system as well as SPFv1.
A further challenge to SenderID has come from Yahoo's DomainKeys system and Cisco's Identified Internet Mail. "These systems are more promising, I think people are cautious about Sender ID's various problems. It breaks down when forwarding, and although there are ways of fixing it, it's far from perfect," said Sargent.
Sender authentication is seen as a way of combating phishing. A Messagelabs report suggested that phishing is set to rise over the next year and become a larger problem than spam. The report claimed that techniques used to fool customers into giving out personal details are in their infancy but are rapidly becoming more sophisticated.