Truncate blacklist (truncate.gbudb.net): what a listing means and how it clears

Truncate is a free DNS blocklist published at the zone truncate.gbudb.net by ARM Research Labs, the company behind the Message Sniffer filtering engine. It is derived from GBUdb, a statistical reputation network built from the traffic that Message Sniffer installations see. An IP is listed when GBUdb's statistics show it sending essentially only unwanted mail — spam, scams, viruses or other malware — with little or no legitimate traffic mixed in.

The important operational fact: the list is maintained automatically. ARM Research Labs' published policy is that there is no manual addition or removal of entries. Entries decay as the IP's statistics change.

What a Truncate listing is, and is not

It is a statement that the traffic observed from your IP was overwhelmingly bad over the sampling window. The name reflects its intended use: the list is designed to be safe to truncate connections on, meaning receivers can reject early with low false-positive risk.

It is not a complaint-based list, a trap-based list, or a judgement about your domain. Truncate is IP-based, and it reflects what a specific filtering network measured.

It is not a list Gmail, Microsoft or Yahoo consult. Its reach is Message Sniffer deployments and servers that have enabled the zone, which skews towards small hosts and corporate mail systems. That makes it a modest direct problem and a strong indirect signal.

How to check

dig +short 9.113.0.203.truncate.gbudb.net      # reversed octets of 203.0.113.9
dig +short -t txt 9.113.0.203.truncate.gbudb.net

An answer in 127.0.0.x means listed. Use the IP from a Received header of real sent mail. ARM Research Labs also publishes a GBUdb lookup for querying an address's current reputation data, which is the authoritative place to look at what the network recorded about your IP.

How the listing clears

1. Stop the traffic that produced it. This is not advice to be patient — it is the entire mechanism. The statistics behind a listing are built from what GBUdb's sensors see; the entry decays once the bad traffic stops and ordinary traffic resumes.
2. Find out what the traffic was. A Truncate listing on an IP you believed was sending normal business mail almost always means something else used it. Check for a compromised mailbox credential, a web form or CMS being abused as a relay, a misconfigured open relay, or an infected host behind the same NAT address.
3. Expect a short decay, not an instant removal. Reported behaviour is a day or two in ordinary cases, longer after a heavy incident. Timing depends on the statistics, not on a queue.
4. If you believe it is wrong, contact ARM Research Labs. There is a published contact path and a GBUdb lookup for reviewing an address's data. What is verified is that the list's maintenance is automated and that no paid or express removal exists. Treat any promise of instant Truncate delisting as a sign to look elsewhere.

The practical reading of a Truncate listing

Because Truncate requires traffic to be almost entirely bad before it lists, a listing on an IP you use for legitimate mail is unusually informative. It is a strong indication that:

• Your IP is also sending something you do not know about, or
• Your legitimate volume from that IP is so low that a small amount of bad traffic dominated the sample, or
• You are sharing an outbound IP with someone whose sending is the problem.

All three are worth a morning of investigation regardless of how many of your recipients query the zone.

What not to do

• Do not hunt for a removal form that matches another list's process. Guides that describe a Truncate ticket queue are describing something else. The policy is automated maintenance.
• Do not pay anyone for a Truncate delisting. There is nothing to buy.
• Do not resume full volume the moment the entry clears. If the cause was a compromise, the receiving side has other reputation data on your IP that recovers more slowly.
• Do not ignore it because its reach is small. The listing criteria mean a listing is rarely noise.
• Do not check the wrong IP. A listing against your office NAT address is a different problem from one against your mail server, though both are worth fixing.

Prevention is the same work as everywhere else

Keep SMTP authentication enforced and credentials rotated, rate-limit any web form that can send mail, keep a separate IP or relay for application mail versus bulk sending, and monitor your own outbound volume so an unexplained spike reaches you before it reaches a blocklist. Those controls prevent Truncate listings and, more importantly, prevent the compromise that produces them.

MailPilot warms mailboxes over OAuth or SMTP/IMAP, checks SPF, DKIM and DMARC, and measures per-provider inbox placement daily — so if an infrastructure problem starts affecting delivery, you see it in placement data rather than inferring it from a blocklist zone with limited reach.