Messaging security and management firm MailKey is launching an authentication technology to fight spam, identity theft and prevent viruses.

The product, SenderID,  works by flagging emails with different levels of authenticity to warn users of the potential dangers associated with them.

SenderID protects against identity theft and address spoofing - both employed by spammers and virus writers to get past filters, a spokesman for MailKey said.

The firm is also developing SenderID Registry; an open directory database for email administrators to register their domains.