AOL, Microsoft and Yahoo are to work together to fight the growing problem of unsolicited commercial email.
The companies promised that the initiative will develop into a broad effort to address spam through an open industry dialogue, driving technical standards and guidelines.
"The time has come for competitors and the industry at large to work together to address the burden of spam," said David Cole, Microsoft's senior vice president of the MSN and Personal Services Group.
"By bringing together different perspectives and expertise, we have a real opportunity to rebuild trust in email."
The companies will work with others in the industry to prevent spammers from using deceptive techniques in email headers.
This can be done by making better use of existing directories of internet addresses, such as the Domain Name System, to locate where email is really coming from.
Email coming from systems determined to be open to unauthorised use, such as open relays, open routers or open proxies, will be stopped.
And email that uses 'concealment techniques' to disguise where it came from will also be restricted.
The group will also endeavour to stop spam being sent in the first place. The companies have promised to work to reduce the ability of spammers to use the email services of AOL, Microsoft and Yahoo to send spam.
The group aims to encourage the adoption of best practices - including eliminating the ability to create fraudulent email accounts in bulk, and defining a mechanism to allow the exchange of consumer complaints and feedback between email providers - by others in the industry.
Law enforcement will also play a part, with the companies working to bolster legal efforts against spammers who rely on "fraudulent means of transmission to circumvent anti-spam filters or otherwise violate applicable law".
Dark matter holds the Universe together - and gravitational waves could help identify it
Addison Lee is working on autonomous taxis for commuting and pleasure
IBM and Technical University of Munich team demonstrate how Shor's algorithm, which can't be cracked by conventional computers, can be solved quickly with quantum computing
Hubble Space Telescope finds superflares from young red dwarfs could strip away planetary atmosphere
Younger stars are 100 to 1,000 times more energetic than when they're older