Blacklists
A Black-list is a database of known Internet addresses
(IP's) used by spammers. Most of the Internet
Service Providers (ISPs) and Bandwidth providers
subscribe to these Blacklist databases in order
to filter out spam sent across their network or
to their subscribers. There are many internet
organizations that specialize in this field.
Many of these
organizations publish Blacklists of mail servers
that are known spammers. Blacklists are used by
thousands of ISPs as part of their Spam defense.
In a skeptical internet communication environment,
a legitimate email system can also end up being
blacklisted, resulting in mail delivery problems
and immeasurable costs in lost business. According
to a study released in August by Return Path,
Inc.'s, Assurance Services division, seventeen
per cent of permission-based email messages get
incorrectly blocked or filtered by the top 12
Internet service providers. Even emails addressed
to confirmed recipients may never reach their
inbox.
Types of Blacklists
IP Blacklist
IP Blacklist blocks specific IP addresses
(and IP ranges), message senders or message recipients
(local mailboxes) as determined in the Blacklists.
The IP Blacklist supports both IP addresses and
subnet definitions. Addresses on the sender/recipient
Blacklist can be defined by the address, simple
wild carded mask or Perl-compatible regular expression.
However, the problem with using an IP Blacklist
is that it may cut off legitimate users trying
to access site or blog or prevent them from sending
email to users.
DNS Blacklist
Domain Name Server (DNS) Black list is a list
of IP addresses that are the source of unsolicited
emails. By taking help of this list, system administrators
can block unwanted domains. They refuse access
to the server and prevent unwanted email messages.
DNS Blacklists are usually maintained by anti-spam
organizations or by individuals.
Spam Blacklist
Spam Blacklists are lists of mail servers
or open relays known to be used by spammers to
deliver unwanted email. By placing these lists
in their mail transport agent's rules system,
system administrators can block spam transmitted
from these sources.
Email
Blacklist
Email Black lists contain known mail servers
and addresses used by spammers. With these lists
in place, access to the server can be denied and
unwanted email messages are discarded. However,
your legitimate emails may also be blocked.
IP blockers
& IP Blackholes
IP Black Hole lists are large repositories
of IP addresses that are known to be spamming.
These repositories use various reporting mechanisms
ranging from human reporting to spam-trap email
boxes to determine who is sending spam, and when
a spammer is identified by IP or IP block, the
spammer is added to the Black Hole list. Other
ISPs and email providers can configure their email
servers to query the Black Hole list any time
a new email comes in. When a new mail arrives
at the server, prior to putting it into the recipient's
mailbox, the server will examine the email, and
trace its origin. Then it will ask the Black Hole
list if this email came from a source that is
a currently-know spammer. If the email does not
originate from a source known to be spamming,
it will be properly delivered into the recipient's
email box. If the mail fails the test and is flagged
as spam, the mail will not be delivered, but rather
will be moved to a storage box for future examination
by either the system administrator or the end-user.
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