Internet Black and White Lists
Table of Contents
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:
- Your messages cannot
be delivered if a recipient's e-mail server checks IP addresses of incoming
connections against black and white lists.
- 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
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 www.spamcop.net. Another one is Open Relay Database,
located at www.ordb.org. Many anti-spam products
also maintain their own black lists and include optional subscriptions
to third-party black list services.
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
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: http://www.dnsbl.info/
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
Replace [IPADDRESS] with your Internet IP address. You can get the correct
value by pressing CTRL+I in PostCast Server or by visiting http://www.myip.com/ 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
- Internet Black and