IP Reputation – the good, the bad and the ugly

by | Jun 4, 2020

Today I’m writing about something that’s not always fully understood and I’m going to do my best to debunk a few myths along the way.

IP Reputation, also known as Server Reputation, used to be one of the most important factors that determined whether or not your emails would reach the inbox. While many other factors now impact deliverability, the server an email is sent from was one of the very first ways the primitive spam filters could decide if the sender could be trusted.

The RACE Model

Firstly, I’ll recap on the four pillars of deliverability that can all affect whether or not the emails that you send will reach the inbox, or whether they’ll be confined to the spam folder. They spell out the word RACE, which stands for:

  • Reputation
  • Authentication
  • Content
  • Engagement

Recap on Reputation

In general, reputation plays a big part on whether your email will be delivered to the inbox. If you, or the email platform you use, have sent emails in the past that have been judged to be unwanted or unsafe, then that information gets filed away by the mailbox providers to be used next time you send more emails.

Now that Authentication is so widely used, it’s the actual email address you use to send your emails that often has the biggest impact on your reputation. As long as you’re using DKIM to digitally sign the emails you send, the sending address in your email will impact what’s known as your Domain Reputation.

The other main form of reputation is IP Reputation, which is based on the IP address of the server that’s sent the email and that’s what we’re looking at today.

What is IP Reputation?

Every computer on the Internet, often known as a server, has one or more unique addresses. Just like the house or apartment that you live in, the address tells the world how to find that server and is unique.

In the Internet world, each server has a name, such as mail.google.com. Each name then gets “looked up” through the Domain Name System and gets converted to a numeric IP address, such as Modern mail servers get set up with lots of IP addresses, so that the load can be spread and also to make it easier to manage their reputation (more on this later).

Mailbox providers then check the IP address used to send every incoming email that they receive, and check one or more databases that are used to record the activity of those IP addresses. That’s how IP reputation works.

Who Monitors IP Reputation?

The major mailbox providers such as Google, Microsoft and Verizon Media no longer use third party databases to monitor IP reputation – they’ve evolved to the point where their machine learning software receives enough data from the billions of emails that they receive to decide for themselves which IP addresses used to send emails are “good” and which ones are “bad”.

There are many other organisations that still maintain their own databases of IP reputation though, by monitoring activity and “scoring” each IP address. Some of these services are still relied upon by many of the smaller mailbox providers, as well as many corporate email servers.

One of the best known external IP Reputation databases is called SenderScore, which is maintained by ReturnPath.

There are other similar services that analyse all the emails sent by individual IP addresses, but these shouldn’t be confused with blacklists which only record details of the “bad” servers (I’ll write more about blacklists in a future article). Blacklists are still very relevant to IP reputation though – if an IP address used to send emails appears on a blacklist, it means that server has sent enough emails that are considered “bad” for one reason or another to have been blacklisted. That’s definitely one indicator of a very poor IP reputation of that server.

What Impact does IP Reputation have?

Although it’s no longer the only game in town, IP Reputation can still have a major impact on whether the email you’ve sent will be delivered to the inbox rather than the spam folder.

If your Domain Reputation is squeaky clean, but the server you’re sending your emails from has a very bad IP Reputation, the chances are very high that your emails will still be treated with suspicion by most mailbox providers, and your emails will end up in the spam folder.

In some cases, if an IP address has a poor reputation, the mailbox providers might “rate limit” or even totally block that IP address. When this happens some or all of the emails you send won’t even get accepted by the recipient’s email servers. In this scenario, you’ll often see this reported as a particular type of “soft bounce” on your email platform. Sometimes it might be reported as a “spam block” or similar; other times it might just be a “temporarily deferred” message. Your email platform might try to re-send these messages a few times, but it’ll have to give up in the end if it can’t get them through.

Different mailbox providers place a different emphasis on IP Reputation.

While the major email providers (Google, Microsoft and Verizon Media) look primarily at domain reputation when deciding whether to deliver emails to the inbox rather than the spam folder, the reputation of the IP address still plays a part and emails sent from a poorer quality IP address are less likely to reach the inbox. 

Some smaller email providers, as well as many corporate servers, still place a much higher importance on the reputation of the IP address and hence can be even less likely to deliver emails to the inbox when they’ve been sent from a poor quality IP address.

From the testing that we’ve done, as well as talking to other deliverability experts, we know that Google places very little emphasis on IP Reputation. So even though Google Postmaster Tools reports on IP Reputation, you’ve got to be sending emails from a “Low” or “Bad” reputation IP address before you’ll start to see problems, and even then, if your domain reputation is still “High”, you might not have too many problems with inbox placement.

In a similar vein, we also know that Microsoft places a much higher emphasis on IP Reputation. So your emails are more likely to be rejected by Microsoft if sent from a server with a poor reputation and it’s much more likely that the emails you send to Hotmail, Outlook.com and Microsoft 365 users will end up in the junk folder unless the reputation of your sending IP address is squeaky clean.

How Can I Maximise my IP Reputation?

This is where it gets very interesting. Unless you manage your own email server, or if your email platform sends from its own dedicated IP address that nobody else uses, you don’t have total control over your IP reputation.

The good news is that every reputable mailbox provider and every reputable email marketing provider invests a huge amount of time, effort and money in protecting the IP Reputation of their servers, so that the emails they send will still get through. Simply put, if they didn’t do that, they’d be out of business because nobody’s going to pay an email provider that can’t get their emails delivered.

Having said that, anyone who sends emails from a shared server that’s also used by other people will be impacting the IP Reputation of that server. Send enough “bad” emails and that server will end up with a poor IP reputation or, worse, end up on a blacklist.

This is why most email providers will very quickly cut off anyone who they suspect of sending spam.

How Do Email Providers Maximise Their IP Reputation?

This is often a very closely guarded secret – but here are a few example of ways that the email providers can protect their IP Reputation.

Filtering out the “bad” emails before they even get sent is one way – if your performance is bad enough, they may even block your sending capability altogether. They may also “silently” stop some of the emails you send from ever going out, for instance if there have been too many soft bounces when sending to certain contacts, or if certain contacts haven’t engaged for a very long time.

Many providers will choose which server to send all your emails from based on their assessment of your sending reputation. Send lots of “good” emails (low bounce rate, very low spam complaint rate and a good open rate) and your emails will be sent from one of their “good” IP addresses; send lots of “bad” emails (high bounce rate, or a high spam complaint rate, or very low open rates) and your emails will be sent from one of their “bad” IP addresses.

It’s becoming more common for email providers to manage things with a much finer granularity though. In these cases, the IP address used to send each email to each individual is chosen based on individual criteria.

As an example, Keap/Infusionsoft uses a sophisticated algorithm when choosing which IP address on a per-email basis. The IP address is chosen based on several criteria, but the key factor that’s taken into account is the “quality” of the contact – how recently has it engaged, and whether the contact is single opt-in (“unconfirmed”) or double opt-in (“confirmed”). The longer is it is since a contact has engaged, the chances are that the emails to that contact will be sent from the poorest quality IP addresses.

What Can I Do?

The quickest answer is very simple – don’t send “bad” emails that might damage your email provider’s reputation and don’t send emails to unengaged contacts.

Ideally, only send emails to contacts that have engaged within the last 30 or the last 90 days. (If you use ActiveCampaign, Infusionsoft or Keap, Deliverability Defender makes this really easy to do).

Don’t complain if you think your ESP is sending your emails from a server with a poor reputation, until you’ve made 100% sure that they’ve no just moved you onto a bad server because of your sending practices.

This is probably a good place to mention the “IP Reputation” report in Google Postmaster Tools. Many people look at Postmaster Tools, see poor IP Reputation in the report and blame the email provider for not looking after their IP addresses. But it’s often their own actions that have led to this, for instance if you’ve been getting a lot of bounces or spam complaints, or if you’ve been mailing lots of unengaged contacts.

One other note if you’re using an email provider that chooses the IP address based on the engagement of the contact (e.g. Infusionsoft) – it’s possible that sending emails to unengaged contacts can become a “vicious circle”. If the contact hasn’t opened an email for a while, it will be mailed from progressively poorer quality IP addresses, which reduces the chance of the email hitting the inbox, which further reduces the chance of the contact re-engaging. So think carefully before trying to re-engage with thousands of “old” contacts that haven’t engaged in months or years.

If you’re using Infusionsoft and need to re-engage with contacts that haven’t opened anything for a long time (this may be because you’ve not mailed them and need to warm them back up), you might choose to consider using WeDeliver.Email. WeDeliver allows you to re-route emails sent to unengaged contacts from Infusionsoft via a third-party email provider that could have a better IP reputation than the Infusionsoft “bad” IP addresses. There are some strong caveats with this though, and I’d always recommend you speak to me before going down that route.

Next Steps

If you’ve not already done so, now would be a great time to run a free Email Health Check – this will show you just how well you’re managing your engagement which often still has an impact on the IP addresses your email provider uses to send out your emails.

Want to make sure your reputation, authentication and engagement are all as good as they can be? You might also want to check out our Email Deliverability Audit, where we go through your entire email setup with a fine toothed comb and make detailed recommendations to help you boost your reputation and maximise the number of people who receive your emails.