IP Address reputation primer

There has been a lot of recent discussion and questions about reputation, content and delivery. I started to answer some of them, and then realized there weren’t any basic reference documents I could refer to when explaining the interaction. So I decided to write some.
This first post is about IP address reputation with some background on why IPs are so important and why ISPs focus so heavily on the sending IP.

Why IP addresses?

ISPs built reputation around IP addresses because it was one bit of data that malicious senders / spammers couldn’t forge. The connecting IP is a fundamental part of the network transaction and if you forge an IP then SMTP can’t work. Because that was the reliable data they had to work with, that’s what they used. Even now, when there are other kinds of data, the IP address is still the first thing the receiving MTA sees.

What is IP reputation?

IP reputation can best be summed up as “past performance is an indicator of future results.” In other words if recipients responded well to mail from an IP address in the past, then they’re likely to respond well to new mail from that IP address.

How is IP reputation measured?

While each spam filtering company and ISP have their own ways of calculating the reputation of an IP address, there are some similarities in what they measure.

  • How many non-existent email addresses is this IP attempting to deliver to?
  • How many abandoned email addresses is this IP attempting to deliver to?
  • How many “known bad” email addresses (spamtraps) is this IP attempting to deliver to?
  • How many recipients complain about receiving this mail?
  • How many recipients complain about not receiving this mail?
  • How respectful of my resources is this IP?
  • Does this IP keep connections open for long periods of time?
  • Does this IP retry deliveries too aggressively?
  • Does this IP stop mailing addresses after receiving a “user unknown” message?
  • Is this IP address configured as if the associated machine was infected by a virus?
  • Is this IP address listed on blocklists we use?

That is by no means an exhaustive list of what ISPs measure. If they can measure it they’ve tried. If the measurement helps them separate spam mail from not-spam mail then they’re using it.

How fast does IP reputation change?

IP reputation is often measured over multiple time periods. ISPs can look at a 1 day, 7 day, 30 day and 90 day reputation. A good analogy is stock prices. Prices can be very volatile in the short term, but more consistent over the long term. A single bad day, where one or more reputation measurements go bad, may affect delivery that day or the next day but won’t damage an overall good reputation. Likewise, a few days of improved mail may not be sufficient to counter months of poor reputation.

How is IP reputation used?

Mail from IPs with a high reputation is accepted faster and at a higher rate than mail from IPs with a lower or unknown reputation.  IP reputation can also influence whether mail is delivered to the inbox or the bulk folder.

Key IP Reputation takeaways

  • IP reputation is about how recipients react to mail from that IP. Happy, content recipients turn into good delivery.
  • Brief changes (for good or bad) don’t necessarily ruin delivery over the long term.
  • Steady improvements will result in improved reputation.
  • It may takes as much time to change a reputation in one direction or another as it took to establish the reputation in the first place.

Next we’ll look at content reputation, how it’s measured and used.
EDIT: A version of this information is available at the Word to the Wise wiki
EDIT: This post was also shared at CircleID

Related Posts

Reputation monitoring sites

There are a number of sites online that provide public information about reputation of an IP address or domain name.

Read More

Permission-ish based marketing

My Mum flew in to visit last week, and over dinner one evening the talk turned to email.

Read More

Email marketing ulcers for the holiday

I’ve mentioned here before that I can usually tell when the big ISPs are making changes to their spam filtering as that ISP dominates my discussions with current and potential clients and many discussions on delivery mailing lists.
The last two weeks the culprit has been Yahoo. They seem to be making a lot of changes to their filtering schemes right at the busiest email marketing time of the year. Senders are increasing their volume trying to extract that last little bit of cash out of holiday shoppers, but they’re seeing unpredictable delivery results. What worked to get mail into the inbox a month ago isn’t working, or isn’t working as well, now.
Some of this could be holiday volume related. Many marketers have drastically increased their mail volume over the last few weeks. But I don’t think the whole issue is simply that there is more email marketing flowing into our mailboxes.
As I’ve been talking with folks, I have started to see a pattern and have some ideas of what may be happening. It seems a lot of the issue revolves around bulk foldering. Getting mail accepted by the MXs seems to be no different than it has been. The change seems to be based on the reputation of the URLs and domains in the email.
Have a domain with a poor reputation? Bulk. Have a URL seen in mail people aren’t interested in? Bulk. Have a URL pointing to a website with problematic content? Bulk.
In the past IPs that were whitelisted or had very good reputations could improve delivery of email with neutral or even borderline poor reputations. It seems that is no longer an effect senders can rely on. It may even be that Yahoo, and other ISPs, are going to start splitting IP reputation from content reputation. IP reputation is critical for getting mail in the door, and without a good IP reputation you’ll see slow delivery. But once the mail has been accepted, there’s a whole other level of filtering, most of it on the content and generally unaffected by the IP reputation.
I don’t think the changes are going to go away any time soon. I think they may be refined, but I do think that reputation on email content (particularly domains and URLs and target IP addresses) is going to play a bigger and bigger role in email delivery.
What, specifically, is going to happen at Yahoo? Only they can tell you and I’m not sure I have enough of a feel for the pattern to speculate about the future. I do think that it’s going to take a few weeks for things to settle down and be consistent enough that we can start to poke the black box and map how it works.

Read More