The SORBS Dynamic User and Host List (DUHL) is similar to other DUL lists. However, many of the others are actually lists of dial-up ranges only. With cable modem and DSL access becoming more prevalent for home subscribers and dial-up becoming correspondingly more rare, the impact of lists of dial-up ranges only is reduced. Therefore, the SORBS DUHL is a list of net blocks where the address space is assigned dynamically to users and hosts regardless of the actual method of connecting those users and hosts to the network. Dynamic assignment of IP addresses makes identification of spam sources a little more difficult. It is a matter of debate as to whether a user at home should be running their own mail server. It is the opinion of SORBS that anyone competent enough to do so should be allowed to run their own mail server, but also, that all outgoing mail from dynamically assigned address space (and in a few cases even from statically assigned space) should be made to flow through the mail server(s) of the Internet service provider in question.

Listing Criteria
SORBS DUHL originally started life as a straight import of the Dynablock list maintained by Easynet NL. Easynet NL stopped providing the list in late 2003.

Requests for entries to be added to or removed from the SORBS DUHL can be made by any Internet service provider responsible for a particular range of IP addresses.

We will also list dynamically assigned address ranges that we come across (most commonly when we receive spam from them). Generic reverse DNS naming is the most important criterion for determining if an address range should be considered dynamically assigned.

Please note that entries in the SORBS DUHL never expire, not even the entries we inherited from Easynet NL Dynablock. We always require contact from the network owner for modifications.

Removals/Deletions from the DUHL
From time to time the DUHL will need to be modified as ISP networks are changed. ISPs are invited to send changes to their address ranges listed.

The general rules of de-listing are as follows:

The Regional Internet Registry (RIR) Point of Contact (PoC) can request a listing or de-listing of any address in their space. The only time this will be refused is when the net block information in the RIR or in the reverse DNS naming clearly indicates the addresses are dynamically assigned (e.g.

Anyone else may request de-listing of addresses or net blocks provided that reverse DNS naming is set to indicate static assignment. SORBS will consider unique names that are not part of a generic naming scheme, or a generic naming scheme with an indication of static-ness (we prefer the word "static" being included in the names, but will accept any existing ISP convention if the ISP just informs us of it) as proof of static assignment. Also, the Times to Live of the PTR records need to be 43200 seconds or more. This is an arbitrary limit chosen by SORBS. And of course, the reverse DNS names need to be valid; i.e. the names given in reverse DNS need to map forward to the IP addresses for which they were given.

End users (non ISP staff): SORBS support staff may ask you to ask your ISP to request the change as you are not authoritative information about the network ranges in question. The SORBS support staff may need to request you change the rDNS naming scheme, so to save time and trouble, ask your ISP to log a ticket and do not log a ticket yourselves.

Please use the support form to submit removal requests.

Additions/Submissions to the DUHL Exclusion List
We also operate a self-help exclusion interface that allows the owner of a system to quickly exclude a single IP address (or, in some cases, multiple IP addresses) from the DUHL. For this to be possible, the following criteria need to be met:
  • The MX record of a domain needs to contain a host name that maps to the IP address involved. The Time to Live of the MX record needs to be at least 43200 seconds.
  • The A record for the host name needs to have a TTL of at least 43200 seconds.
  • The reverse DNS PTR record for the IP address involved needs to map back to the name given in the MX record, and to have a TTL of at least 43200 seconds.
  • If there are multiple MX entries, these rules apply to them all.
When all these conditions are met, please go to to request quick exclusion for your mail server.

Additions/Submissions to the DUHL
Unfortunately SORBS is unable to safely determine whether a request for submission to the DUHL is coming from the network owner, so the submission system is mostly manual.

For DUHL additions please use the mail form to log a DUHL Nomination Ticket.

Copyright © 2002-2023 by SORBS | Terms & Conditions | Privacy Policy