The Messaging Anti-Abuse Working Group (MAAWG) has published guidelines that should help internet service providers improve the way they fend off spam attacks.
The group suggests that ISPs should block the "port 25" which misfits often use to send spam; also on the check list is the use of separate servers for emails received and for those being forwarded.
It is estimated that 90 percent of spam which is sent by botnets could be stopped simply by closing this port.
Other measures enunciated included policies on how to tackle bot behaviour coherently as well as how to handle emails send by hosts with dynamic IP addresses and more.
More about the group's working - which comprises of more than 230 abuse and privacy professionals from ISPs, email providers and vendors representing 18 countries - can be found here.