If you were sent to this page because of a bounced email message, please look up the error code from that message and click the appropriate link from the table below for an explanation of why the email was rejected.

If you are simply interested in some general information on the way DNS-based blackhole lists and other spam blocking tools are used in Dyn email services, see the General Dyn Email Spam Blocking Information section.

Code Basic Explanation
DYN-001 The recipient’s address is not listed in the service’s user list. More Information
DYN-002 Your IP address is listed on an internal Dyn blacklist due to large volumes of spam. More Information
DYN-501 Your message contained URLs known to Dyn to be used in spam. More Information
PBL-001 Your IP address is listed on the Spamhaus PBL. More Information
RDNS-001 Your IP address does not have valid reverse DNS. This often indicates a simple misconfiguration. More Information
SBL-001 Your IP address is listed on the Spamhaus SBL. More Information
SCBL-001 Your IP address is listed on the SpamCop Blocking List. More Information
SORBS-001 Your IP address is listed on the SORBS DUL. More Information
XBL-001 Your IP address is listed on the Spamhaus XBL. More Information

General Dyn Email Spam Blocking Information

One of the many features of Dyn inbound email services is spam blocking. As a responsible email service provider, we feel it is necessary to protect our customers from spam, and one of the methods we use to do that is with various DNS-based blackhole lists, or DNSBLs. Through the use of a carefully selected set of DNSBLs, we can help block a significant percentage of incoming spam before it uses significant system resources, without blocking any legitimate customer email.

Some of the lists and spam blocking options below are applied automatically to all email transiting through the Dyn email servers, while others are optional and may be selected by customers on a per-domain basis.

Dyn Email User List

Dyn Email Backup MX and Dyn Email Gateway feature a user list, allowing customers to specify exactly which mailboxes exist at their email server. This allows Dyn email to filter out email destined to invalid addresses. If the destination email address should exist, but you are receiving this error, contact the customer through another method and ask them to ensure their user list is properly configured.

Dyn Blacklist

Dyn maintains an internal blacklist of repeat spam offenders, based on log information from our email servers. We are careful to ensure that this list includes only true spam sources, but if you feel your email has been blocked improperly, see the Appeal Information section, below.

Dyn URL Blacklist

Dyn maintains an internal blacklist of URLs frequently used in spam, and uses this list to protect our customers. If you feel that your email has been blocked improperly, see the Appeal Information section, below.

Spamhaus PBL

The Spamhaus PBL is a DNSBL database of end-user IP address ranges which should not be delivering unauthenticated SMTP email to any Internet email server except those provided for specifically by an ISP for that customer’s use.

Reverse DNS Verification

Spammers often use hosts that do not have valid reverse DNS (the mapping from an IP address back to a hostname) in an attempt to obscure their tracks. Some customers block all email that comes from hosts without valid reverse DNS. You generally will need to contact your ISP to inquire about having your reverse DNS entry fixed if you are finding email blocked due to this restriction.

Spamhaus SBL

The SBL is a realtime database of IP addresses of verified spam sources (including spammers, spam gangs and spam support services), maintained by the Spamhaus Project team and supplied as a free service to help email administrators better manage incoming email streams.

SpamCop Blocking List

This text taken from What is the SpamCop Blocking List (SCBL)?

The SCBL is a list of IP addresses which have transmitted reported email to SpamCop users, which in turn is used to block and filter unwanted email. The SCBL is a fast and automatic list of sites sending reported email, with a number of report sources, including automated reports and SpamCop user submissions. The SCBL also quickly and automatically delists these sites when reports stop.

The SCBL aims to block spam with minimal blocking or misidentification of wanted email. Given the power of the SCBL, SpamCop encourages users to also actively maintain a whitelist of wanted senders of email. SpamCop also encourages SCBL users to tag and divert email, rather than block it outright. In the end, most SCBL users find that the amount of unwanted email successfully filtered makes the risks and additional efforts worthwhile.

Due to the automated nature of this DNSBL, Dyn considers it to be to be “high risk”. Please use this list with caution.


The SORBS DUL (also known as the DUHL) lists dynamic IP addresses
assigned to modems, DSL lines, cable modems, etc. Dynamic IP assignment makes spam tracking more difficult, and most (if not all) dynamic IP users have a email server provided by their ISP, on a static IP address, which they can use to relay their legitimate email.

If your IP is listed on this list, you can send email to customers blocking with this list by using your ISP’s email server instead of sending the email directly to our servers.

This DNSBL is considered “high risk” by Dyn, as blocking all dynamic IP space can result in a somewhat significant false-positive rate. Please use this list with caution.

Spamhaus XBL

The Spamhaus Exploits Block List (XBL) is a realtime database of IP addresses of illegal 3rd party exploits, including open proxies (HTTP, socks, AnalogX, wingate, etc), worms/viruses with built-in spam engines, and other types of trojan-horse exploits.

Dyn Appeal Information

If you believe your email has been blocked incorrectly by one of the Dyn administered lists, and you are the administrator or owner of the IP address(es) or other resource(s) in question, please send an email to abuse (at) dyn [dot] com, including the IP address(es) or other resource(s) being blocked, the full block error message, and any other details explaining why you do not feel the message should have been blocked.

Please do NOT contact us regarding any of the other lists – they each have their own listing and removal policies. We use their data, but we cannot remove or change their listings.