A Dial-up/Dynamic User List (DUL) is a type of

DNSBL A Domain Name System blocklist, Domain Name System-based blackhole list, Domain Name System blacklist (DNSBL) or real-time blackhole list (RBL) is a service for operation of mail servers to perform a check via a Domain Name System (DNS) query whe ...

which contains the

IP addresses An Internet Protocol address (IP address) is a numerical label such as that is connected to a computer network that uses the Internet Protocol for communication.. Updated by . An IP address serves two main functions: network interface ident ...

ISP An Internet service provider (ISP) is an organization that provides services for accessing, using, or participating in the Internet. ISPs can be organized in various forms, such as commercial, community-owned, non-profit, or otherwise private ...

assigns to its customer on a temporary basis, often using

DHCP The Dynamic Host Configuration Protocol (DHCP) is a network management protocol used on Internet Protocol (IP) networks for automatically assigning IP addresses and other communication parameters to devices connected to the network using a cli ...

or similar protocols. Dynamically assigned IP addresses are contrasted with static IP addresses which do not change once they have been allocated by the service provider. DULs serve several purposes. Their primary function is to assist an ISP in enforcement of its

Acceptable Use Policy An acceptable use policy (AUP), acceptable usage policy or fair use policy is a set of rules applied by the owner, creator or administrator of a computer network website, or service. That restricts the ways in which the network, website or system m ...

, many of which prohibit customers from setting up an

email server Within the Internet email system, a message transfer agent (MTA), or mail transfer agent, or mail relay is software that transfers electronic mail messages from one computer to another using SMTP. The terms mail server, mail exchanger, and MX host ...

. Customers are expected to use the email facilities of the service provider. This use of a DUL is especially helpful in curtailing abuse when a customer's computer has been converted into a

zombie computer In computing, a zombie is a computer connected to the Internet that has been compromised by a hacker via a computer virus, computer worm, or trojan horse program and can be used to perform malicious tasks under the remote direction of the hac ...

and is distributing email without the knowledge of the computer's owner. A second major use involves receivers who do not wish to accept email from computers with dynamically assigned email addresses. They use DULs to enforce this policy. Receivers adopt such policies because computers at dynamically assigned IP addresses so often are a source of spam. The first DUL was created by Gordon Fecyk in 1998. It quickly became quite popular because it addressed a specific tactic popular with spammers at the time. The DUL subsequently was absorbed by

Mail Abuse Prevention System The Mail Abuse Prevention System (MAPS) is an organization that provides anti-spam support by maintaining a DNSBL. They provide five black lists, categorising why an address or an IP block is listed: * Real-time Blackhole List (RBL), the one for wh ...

(MAPS) in 1999. When MAPS was no longer a free service, other DNSBLs such as

Dynablock Easynet was a managed services provider and delivered integrated networks, hosting and unified communications services to organisations globally. The company was later renamed Easynet Global Services, and a sister company, Easynet Connect, was fo ...

Not Just Another Bogus List Not Just Another Bogus List (NJABL) was a DNS blacklist. NJABL maintained a list of known and potential spam sources (open mail relays, open proxies, open form to mail HTTP gateways, dynamic IP pools, and direct spammers) for the purpose of being ...

(NJABL), and

Spam and Open Relay Blocking System SORBS ("Spam and Open Relay Blocking System") is a list of e-mail servers suspected of sending or relaying spam (a DNS Blackhole List). It has been augmented with complementary lists that include various other classes of hosts, allowing for cu ...

(SORBS) began providing lists of dynamically assigned IP addresses.

References

{{Reflist Internet access