I am writing an antispoofing patch for qmail .

In some cases you want that some from adresses are only from a particular
subnet or ipadress.
It works a bit like badmailfrom.
When a domain or emailadress is related with some subnets , using a from
address from another subnet will be impossible.

It is still in experimental fase and I should do some tests.

an antispoofing control file looks like this:

foo.be: 10.10.42/255.255.255.128
bar.be: 10.148.249 10.134.45.2/255.255.255.0
dany@fee.org: 10.148.249/255.255.255.0

In this case the givn domains can only come from the defined ipadresses.

Every other domain is allowed.