September 12, 2018

Deliverability 101: What’s the difference between spam trap networks and sensor networks?

If you’ve read our Deliverability Guide, you already have some understanding of what spam traps are and how they operate. A collection of these is called a spam trap network. Similarly, we also touch upon sensor networks in our guide. Even to a seasoned email marketer, these concepts can become confusing. We’re not down with that. Let’s take a quick look at the different types of spam traps, how they work as a network, and how an email marketer should think about them.

As a review, there are three types of spam traps: Pristine, typo, and recycled.

Pristine traps

are email addresses at domains never used to receive email for actual human recipients. Thus, they would never have signed up to receive email from any sender. Typo traps are email address at domains that closely resemble real domains, like or Recycled traps are email addresses once actively used by real recipients, but have been dormant, abandoned, or terminated for an extended period of time.

Spam Trap Networks

Spam trap networks are collections of thousands or millions of such addresses existing solely to collect data about the messages they receive as well as data about the senders who sent those messages. They collect information like sending IP, sending domain, and even message-level data like subject line and content.

Spam trap networks can either be used by ISPs to inform the reputation systems that make spam filtering decisions (reputation-impacting networks), or they can be used to relay information back to senders to help them identify weaknesses in their address acquisition strategy and list hygiene (sensor networks).

Here’s where it gets a little complicated: Sensor networks are comprised of spam traps, but they behave differently than a typical spam trap network. So we’ll start with a typical spam trap network, or reputation-impacting network.

Reputation-Impacting Networks

Analyzing the list of email addresses someone is sending to is a very reliable way to identify (and block) malicious senders. Why? Spammers are very bad at collecting email addresses. They will take just about any email address they can get their hands on and start sending email to it.

The addresses they send to are often very old (recycled traps), misspelled (typos), or purchased and scraped from just about anywhere on the web (pristine). Years of analysis has shown that senders with lists containing a large number of these addresses are very likely to send messages that recipients do not want. As a result, many ISPs have spun up spam trap networks that they use to improve their ability to catch spammers. ISPs that don’t run their own spam trap networks often partner with private operators and use that data to inform their spam filtering decisions.

In addition to being used directly by ISPs, these spam trap networks are also the primary source of data for most of the email blacklists out there. If a sending IP or sending domain sends too much mail to their network of spam traps, the IP or domain will be listed as a likely source of spam. These lists of spammy IPs and domains (blacklists) can then be used by ISPs to supplement their spam filtering decisions

Now, we can get back to the less typical spam trap network…

Sensor Networks

250ok operates a sensor network. We own and operate millions of spam traps across thousands of domains. When a message lands in one of these inboxes, we log the IP that sent it, along with a bunch of other data like subject line, and “from” address. The data from our spam traps is not used to feed any reputation algorithms or email blacklists. Instead, we relay that data back to our users.

That’s the distinguishing difference between spam trap networks and sensor networks: Reputation-impacting spam trap networks provide value for ISPs, and sensor networks provide value for senders.

You may be wondering why should you care about hitting spam traps in a sensor network that doesn’t hurt your reputation and won’t cause blacklistings?

Well, if you are hitting traps in a sensor network, you are also hitting traps in a reputation-impacting network. The great thing about 250ok’s sensor network is that we tell you about the spam traps you hit. This gives you an opportunity to evaluate the data we send back to you and make appropriate changes to your sending and list acquisition strategies.

You can relax, though. Every sender hits spam traps, and very few senders aim to hit zero spam traps. The goal should be to find your baseline (how many traps you hit on an average day or week) and work towards reducing that number over time. If your email program is performing at a high level and you are happy with your results, you can use the spam trap data provided by 250ok to monitor changes in your sending and list acquisition strategy.

A good place to start is to identify which of your sending IPs or sending domains are hitting the most spam traps relative to sending volume. Using data available within 250ok’s Reputation, you can even determine which subject lines are hitting the most traps. This makes it much easier to identify areas for improvement in your email program. Of course, that’s just the start, and we could go on, but we’ll let you go here. Until next time!

Author: Luke Martinez

Luke is a deliverability expert with a passion for getting email to the inbox. With more than four years at SendGrid prior to joining 250ok, his intimate understanding of the email ecosystem, email protocols, and marketing best practices allows him to provide data and insights that drive engagement and results from email programs both large and small.

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