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Internet Black and White Lists

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Two of the least effective and most damaging methods for fighting spam are white lists and black lists. In many cases, these lists harm innocent people and prevent critical business e-mail from being delivered. One of the drawbacks is that if you block an entire domain, you may be blocking as much as 90 percent of wanted e-mail while blocking only 10 percent of unwanted spam.

If you are sending e-mail from an e-mail server on your computer and your IP address is on one of the lists, that can affect you in two ways:

  1. Your messages cannot be delivered if a recipient's e-mail server checks IP addresses of incoming connections against black and white lists.
  2. If your messages are successfully delivered to recipients, they can run an anti-spam software that uses black lists to categorize your messages as spam. Your e-mail can end up in a folder for spam or be deleted and will probably never be read.

Black lists

A spam black list is a list of IP addresses and domains of known spam e-mail servers. Black lists are used to block all e-mail that comes from certain servers on the Internet that have been identified as being used to send spam.

A well-known black list is hosted by SpamCop, located at Another one is Open Relay Database, located at Many anti-spam products also maintain their own black lists and include optional subscriptions to third-party black list services.

White lists

White lists are the opposite of blacklists. They list trusted e-mail addresses and domains that are always allowed to send e-mail, no matter what the content is. White lists are used to require that senders authenticate their identity prior to e-mail being delivered to the recipient. White lists will definitely allow e-mail coming from a trusted site to come through, but do not provide a solution for blocking spam. White lists require constant maintenance to be very effective. If not properly maintained, the risk of losing e-mail from legitimate sources is high.

Dial-up Lists (DUL)

Some ISPs block access to their servers if the incoming connections originate from dynamic IP addresses. Their goal is to force users that are running e-mail servers on their dial-up connections to send all outgoing e-mail through their ISP's e-mail server. If you send messages from PostCast Server using a dial-up connection, you will probably experience this problem with AOL.

A well-known DUL list is MAPS Dial-up User List:



PostCast Server has a feature that allows you to check if your computer's IP address is blacklisted. The program uses a DNSbl service that lets you check whether a particular IP address is being blocked by any of more than 100 anti-spam services:

Open the Setup Wizard from the Tools menu and press the "Blacklisted IP" button in the Network Diagnostics step:

You can also see the status of the IP address you are using if you visit this location:[IPADDRESS]

Replace [IPADDRESS] with your Internet IP address. You can get the correct value by pressing CTRL+I in PostCast Server or by visiting web site.



If you are using a dial-up connection, usually a few anti-spam services have your IP in their lists. If you discover that a significant number of black lists have your IP address, you have these options:

Establish a new connection

Establish a new dial-up connection to your ISP. That usually results in assigning a different Internet IP address to your computer. Run the test again to see if the new address is also blacklisted.

Use a different ISP 

You can use a different ISP to connect to the Internet. Each ISP has its own range of IP addresses they assign to dial-up users. There is a good chance that the IP addresses of a different ISP are not blacklisted. Here are some web sites that can help you find thousands of ISPs:

Ask your ISP for a static IP address outside of the dial-up space


Ask the list maintainers to exclude your host


Use socks proxy servers

You can send e-mail using the socks proxy access to a computer on the Internet. This feature enables you to relay e-mail through other servers. When the message is sent using a third-party socks proxy, your IP address does not appear as the source of the message.

The best solution is to connect to your ISP's socks proxy directly if it is provided by the ISP. Their server's (non-dynamic) IP address will be the source of your outgoing messages. For more information, see Firewall and Proxy Support.

Use backup SMTP servers

The professional edition of PostCast Server has a feature that allows you to specify one or more backup SMTP servers. If only certain domains are unable to receive messages from PostCast Server, you can use this option to forward those messages to your ISP's SMTP server. Open the Settings/Undelivered/Gateways window to configure this feature. For more information, see SMTP Gateways.

Anti-Spam Methods:

  1. Overview
  2. Port 25 Blocking
  3. Internet Black and White Lists
  4. Blocking Open Relays
  5. DNS Lookups
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