Marketing Tips

Deep Dive into Sender Reputation

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One of the most common questions email deliverability professionals get asked is, “How do I improve my sender reputation if all my mail is spamfoldered?” Before we can answer this question, we first need to understand email sender reputation.

Email sender reputation is how mailbox providers (MBPs) identify you as a legitimate sender. Each time you send an email campaign, MBPs collect important data that says whether you follow proper sending practices. The better your sender reputation, the more likely a MBP will deliver your emails to the inboxes of recipients on their network. A poor sender reputation could mean your mail is getting sent to spam instead of the inbox, which would negatively impact your email marketing ROI.

In this blog post, we’ll dive deeper into email sender reputation, the factors that affect it, and steps you can take to start improving your reputation and increasing revenue.

Your IP reputation is like your credit score

There are two key components of email sender reputation – the first is known as IP reputation.

In the early 2000s, spammers were trying new techniques to avoid spam filters (the most famous being snowshoe spam) and MBPs had to go beyond static blocklists and safelists to curb the spam. This led to the birth of IP reputation, as the connecting IP was one of the reliable parts from the mail headers.

We can think of IP reputation the same way we think of a credit score: the higher the score, the better the chances of making it to the inbox. A new IP starts with a neutral reputation. Based on the positive and negative signals that an IP exhibits, the reputation could either improve or deteriorate.

For example, if the reputation is scored on a scale of one to nine – one being good and nine being poor – the new IP would start at five. Its reputation would then change based on the signals a sender exhibits.

Here are some of the signals senders exhibit that determine IP reputation and email deliverability.

IP reputation signals:

  • Opens
  • Trusted recipient volume
  • Address book hit
  • Not spam report
  • Low spam complaints
  • Spam complaints
  • Spam traps
  • Bounces
  • Delete without open
  • Unsubscribes
  • IP netblock/ASN
  • Second received header
  • DNS checks – A/MX/PTR (fully qualified reverse DNS)

IP reputation is a great way for MBPs to rate limit email volumes, especially during spam runs or DDOS attacks on their servers. If you see a drop in your sender reputation, remember MBPs will spamfolder emails for a fixed time before you start seeing temporary failures ( errors).

A temporary failure, or deferral, is an early signal that notifies a user when they are having reputation issues. As a sender, it is important to look at both a drop in your engagement rates, as well as a spike in deferrals.

Your brand takes precedence for domain reputation

As mentioned earlier, IP reputation is a good defense mechanism for obvious spam mails and spam runs, but spammers are an ingenious bunch (duh!). They figure there are quite a few trusted IPs they can piggyback their malicious mail onto.

A couple of years ago, most spam was from free webmail accounts. IPs belonging to these servers tend to have a good reputation or can be found on most of the receivers’ allowlists. Anti-spam professionals realized they needed to supplement IP reputation along with domain reputation and look for additional signals to feed into the reputation algorithm.

Your domain reputation is based on your sending domain instead of your IP address. This means that your brand takes precedence when it comes to MBP filtering decisions.

There was also a push in authentication around this time (IPv6 adoption accelerated this, too) and we see more and more email service providers (ESPs) signing emails with security protocols like DKIM and DMARC. Email authentication helped in reducing usual “From” address spoofing, and receivers had a few domains in the headers that they could rely on.

Domain reputation signals:

  • DKIM “d=” domain – RFC5322
  • From address/domain
  • Return-path domain
  • Authentication results – Domain-based alignment
  • ARC headers
  • Message body URLs
  • Message content
  • X-headers – added by ESP
  • List unsubscribe
  • Engagement – Open rates, click rates, click to open, etc.

How to improve email sender reputation

Most major MBPs have either IP reputation or domain reputation in their arsenal to combat spammers. So, if you have hit rock bottom at an MBP, how can you improve your email sender reputation? Here are a few tips to get you started.

1. Monitor KPIs.

Most reputation issues arise due to a lack of monitoring. Have a check on ESP dashboard for KPIs like email delivery rates, complaint rates, unsubscribes, and engagement rates. You can also utilize Validity tools like reputation monitoring for spam traps, Universal Feedback Loop, seedlist testing to check mail placement, and DMARC to ensure a spoofer is not derailing your email program.

2. Reduce send volume.

The first step to improve sender reputation is to cut back on the volume of mail being sent. This is helpful at MBPs where IP reputation has higher influence. The lower the reputation, the lower the threshold of accepted mail volume.

3. Remove old or unengaged addresses.

Mailbox providers like Gmail are more reliant on engagement data, so restricting sending to less than 90-day openers would yield better results. This article should provide a good idea on how to sunset older addresses.

4. Do a post-mortem of the drop in reputation.

The last thing you want to do is continue the older practices you had in place which caused the drop in reputation. Check for the source of the issue. Is it a recent poor list that caused higher bounces and unsubscribes? Is it a gradual drop in reputation due to hitting a high volume of recycled spam traps and lower engagement? Take necessary actions like subscribing to Google Postmaster Tools for additional data points, or utilize Validity list cleaning to reduce the number of invalid addresses. Add a sunset strategy for old addresses and put eligible candidates in a re-engagement campaign.


Maintaining a good sender reputation is a continuous process, and it can prepare your marketing program to handle spikes in email volume. By utilizing an all-in-one deliverability solution like Everest, you can proactively monitor and manage all the signals affecting your sender reputation, enabling you to reach more people and achieve your ROI goals.