MailHop Spam Blocking Information

If you were sent to this page because of a bounced e-mail 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 e-mail 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 DynDNS.com's MailHop® services, see the General MailHop 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 DynDNS.com blacklist due to large volumes of spam. More Information
DYN-101 Your IP address is listed on the DynDNS.com Spamikaze DNSBL due to messages sent to internal spamtraps. More Information
DYN-501 Your message contained URLs known to DynDNS.com 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
RFCI-001 Your IP address is listed in abuse.rfci-ignorant.org. More Information
RFCI-002 Your IP address is listed in bogusmx.rfci-ignorant.org. More Information
RFCI-003 Your IP address is listed in dsn.rfci-ignorant.org. More Information
RFCI-004 Your IP address is listed in postmaster.rfci-ignorant.org. More Information
RFCI-005 Your IP address is listed in whois.rfci-ignorant.org. 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 MailHop Spam Blocking Information

One of the many features of the DynDNS.com MailHop services is spam blocking. As a responsible mail 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 e-mail.

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

MailHop User List

MailHop Backup MX and MailHop Relay feature a user list, which allows customers to specify exactly which mailboxes exist at their mail server. This allows MailHop to filter out mail 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.

DynDNS.com Blacklist

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

DynDNS.com Spamikaze DNSBL

DynDNS.com maintains an internal blacklist using "Spamikaze" software based on messages sent to internal spamtraps. These are addresses which never receive valid e-mail. IPs on this list expire over time, but will remain indefinitely if they continue to send mail. You can use the lookup link below to find the times your IP sent mail to our spamtraps, and request removal, but if it continues to send mail to the spamtraps, it will be re-listed very quickly.

DynDNS.com URL Blacklist

DynDNS.com maintains an internal blacklist of URLs frequently used in spam, and uses this list to protect our customers. If you feel that your mail 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 mail 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 mail 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 mail blocked due to this restriction.

RFC-Ignorant: Abuse

The RFC-Ignorant Abuse DNSBL is a domain-based DNSBL, which lists domains that do not accept mail to abuse@domain.tld, as required by RFC2142. All organizations with e-mail, or any other abusable Internet services, must have a functional abuse contact address.

DynDNS.com considers this to be a high-risk DNSBL, as there are many high-profile domains (such as aol.com) that are frequently present on this list. Please use this list with caution.

RFC-Ignorant: Bogus MX

The RFC-Ignorant Bogus MX DNSBL is a domain-based DNSBL, which lists domains that have any invalid MX records (per the relevant specifications) listed in DNS. Please see the listing policy (linked below) for more details on the criteria. These domains are likely unable to accept mail, and thus should not be used to send mail.

RFC-Ignorant: DSN

The RFC-Ignorant DSN DNSBL is a domain-based DNSBL, which lists domains that refuse to accept mail with the originator given as <>. This originator, sometimes referred to as the "null sender", is typically used for bounces generated by mail servers, and must always be accepted per the SMTP specifications.

DynDNS.com considers this to be a high-risk DNSBL, as there are many legitimate domains that block DSN as a (misguided) anti-spam measure. Please use this list with caution.

RFC-Ignorant: Postmaster

The RFC-Ignorant Postmaster DNSBL is a domain-based DNSBL, which lists domains that do not accept mail to postmaster@domain.tld, as required by RFC2821. See the listing policy (linked below) for more details on this list.

DynDNS.com considers this to be a high-risk DNSBL, as there are many high-profile domains (such as hotmail.com) that are frequently present on this list. Please use this list with caution.

RFC-Ignorant: WHOIS

The RFC-Ignorant WHOIS DNSBL is a domain-based DNSBL, which lists domains that do not provide valid contact information in WHOIS. The criteria for this list are sometimes quite broad, please see the listing policy (linked below) for full details.

DynDNS.com considers this to be a high-risk DNSBL. Please use this list with caution.

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 mail, 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, DynDNS.com considers it to be to be "high risk". Please use this list with caution.

SORBS DUL

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 mail server provided by their ISP, on a static IP address, which they can use to relay their legitimate mail.

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

This DNSBL is considered "high risk" by DynDNS.com, 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.

DynDNS.com Appeal Information

If you believe your mail has been blocked incorrectly by one of the DynDNS.com-administered lists, and you are the administrator or owner of the IP address(es) or other resource(s) in question, please send an e-mail to abuse (at) dyndns [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.