Refuse Host and Network

Question

How is it that I'm still receiving email from an ip address that I have blocked?
In Server Admin, in the Mail services/Settings/Relay pane I have refused an ip address range (actually many) in the "Refuse all messages from these hosts and networks" field, and still email within that range continues to get through. For example I have refused a range formated as such; x.x.x.x/8. Low and behold, in comes an email from x.xx.xxx.xx.
Any idea's why it doesn't always work?
TIA

Answer 1

You can do three things, assuming you can define what "network" means to you.
The simple one is to change them into int or BitSet and then XOR them. The position of the first set bit from the high order side tells you "how different" the two IPs are, and then you'll have to decide how many octects of the IPs specify your actual network.
An alternative is to define a network boundary, for example a good guess is that 192.168.1.0 to 192.168.1.255 is your home network, but if you have a router you might want to go from 192.168.1.0 to 192.168.2.255, depending on your settings, and then you'll have to match an IP to see if it falls into the boundaries of your network.
The third is to get hold of your adapter's network mask and AND it with an IP. If the result is the same that you obtain by ANDing the network mask with your IP, then the two are in the same network.
Example:
int networkMask = 0xffffff00;  // 255.255.255.0
int myIP = 0xc0a8164; // 192.168.1.100
int otherIP = ?;
if ( myIP & networkMask == otherIP & networkMask) {
    // yep, same network(I might have screwed up the network order here, I never remember which is which, but I believe it's little endian, so it should be OK)