When an IP address (dynamic or fixed ) is reported for sending spam it's added to a blacklist. There are three different types of blacklists:

Temporary An IP address placed on a temporary blacklist will have email coming from that IP address blocked for several hours. After a few hours offending IP address is removed from blacklist.

Permanent When an IP address is added to a permanent blacklist any email server configured to block email from this list will never receive email from that range of IP addresses again.

Comprehensive This is most damaging of blacklists. Not only does it block a single IP address it also blocks IP addresses next to it. For example if IP address 192.156.66.67 was added to a comprehensive blacklist then all IP addresses close to 192.156.66.67 will also be blocked. This can be a huge problem for those website owners using virtual hosting because if your host has ever appeared on a blacklist then you're also on same blacklist, by default, because of shared hosting from same IP range. It's important for all website owners to check whether or not they're on a blacklist. You'll need your IP address (available from your webhost) and you can check your blacklist status at: www.mail-abuse.org/cgi-bin/lookup

Blacklists are a necessary evil due to volume of spam being sent each day but are not an exact science. Take a few moments from your day and ensure that your website or email address is not being blocked.

But..... CanSpam Act 2003... surely that's going to make a difference? Of course.

Any ISP in United States can get in serious, serious trouble for signing pink contracts. Problem is that there's a whole big world wide web out there and vast majority of pink contracts are signed with overseas ISPs where US authorities have no jurisdiction - China and Russia being perfect examples.

There's no moral to this story. Spam is a huge problem that's finally being taken seriously by Governmental bodies. However until they start imposing prison sentences or seizure orders on those individuals and companies in pink contract business problem can only continue.