I've read a few articles on this SPF idea...

http://spf.pobox.com

does seem to make sense, especially if AOL are starting to use it and some academic sites.

at its simplest level, you put a record in your DNS for external sites to check against.

this then defines either your IP real address range (to stop spam/ faked virus emails etc) or you explicitly define the servers that you send mail from.

this is all makes a lot of sense to me.

it doesn't have a "critical mass" yet, enough people to make it meaningful, but in the next few months with new releases of software.

comments?

thanks Roberto.

even if your own site doesn't use it, I can see the advantages in catching spoofed emails and viruses if others do (especially AOL).

if you run up nslookup, set type=txt, and lookup lboro.ac.uk you will see an example.

something like

"v=spf1 ip4=158.125.0.0/16 ip4=131.231.0.0/16 ip4=194.66.220.0/24 ip4=21
3.106.251.0/26 ip4=213.106.253.0/26 ?all"

so you know exactly what their valid subnets are, anything else can be ditched.

the subnet idea is good, you can even be specific to your 3-4 servers that send outgoing mail which is probably even better.