If you're trying to send email to somebody and your message was returned with an error message referencing this site, your intended recipient's mail server most likely rejected the message based on your mail server's or your computer's IP address being in the list we maintain. This is most likely due to your mail server being misconfigured as an open relay or your computer's IP address being listed as a dynamic/dial-up IP. In most cases, this means your Internet Service Provider needs to be informed, as they will need to secure their mail server and have it removed from the list or make provisions to accept mail from your computer even though your IP is in our list. If you or your organization run your own mail server, you'll have to inform whoever maintains your mail server so they can fix it and remove it from the list.
If you're having trouble receiving email from people who used to be able to send you email, it's possible your ISP or whoever runs the mail server your mail is delivered to is using our list or one or more of several dozen other anti-spam dnsbls. Without seeing the exact error message received by the person who tried to email you, it's impossible to say if the server they send their email through is in our list or any other list. In this case, your best bet is to contact the ISP who's mail server appears to be listed and notify them of the problem. They will have to deal with whatever problem caused their system to be listed, find out which lists they're in, and do what they can to get off of them.
Again, we do not block email. Mail server administrators may use the information we maintain to either tag or reject email on their servers. This is a policy decision they have made. If you object to the idea of your mail being rejected just because it goes through an open relay or other type of spam source, contact your Internet Service Provider or those who maintain the system that rejected your email. We cannot change their policy.
Do not send us email complaining about this. We cannot help you. Only the people who maintain the misconfigured mail server can fix the problem. In most cases, this means you should forward the error message to your service provider or your organization's IT staff. That way they can contact us if necessary, fix their mail server, and remove their mail server's IP from the list.