When a B2B software company asked me to audit their email deliverability, the first thing I checked was their Sender Score. It was 62. Not terrible, but not good either. They were sending from a reputable email service provider, their authentication was perfect, and their content was professional. So why the mediocre score?
The answer was in their sending patterns. They'd send nothing for weeks, then blast 50,000 emails when they had a product announcement. This inconsistency made them look unpredictable to ISPs. Their complaint rate was also creeping up—not dramatically, but enough to drag down their score over time.
Sender Score isn't the only reputation metric that matters, but it's one of the most visible. Understanding what drives it helps you understand what drives deliverability more broadly.
What Sender Score measures
Sender Score is a reputation rating developed by Validity (formerly Return Path). It assigns a number from 0 to 100 to every IP address that sends email, based on observed sending behavior. Higher scores indicate better reputation; lower scores indicate problems.
The score is calculated from multiple signals. Complaint rates—how often recipients mark your email as spam—are heavily weighted. Unknown user rates matter too; sending to many invalid addresses suggests poor list quality. Spam trap hits are particularly damaging. Volume and consistency patterns factor in. External blacklist appearances affect the score.
Think of it as a credit score for email. Just as a credit score predicts whether you'll repay a loan, Sender Score predicts whether your email is wanted. ISPs use this prediction (among other factors) to decide whether to deliver your email to the inbox, filter it to spam, or reject it entirely.
The score updates regularly based on recent sending behavior. A bad week can drop your score; consistent good behavior raises it. This responsiveness means you can recover from problems, but also that you can't rest on past performance.
How ISPs use reputation data
Sender Score itself is one input among many that ISPs consider. Gmail, Microsoft, Yahoo—they all maintain their own reputation systems with their own algorithms. But the underlying signals are similar.
When your email arrives at an ISP, they check multiple reputation sources. They look at their own historical data about your IP and domain. They might query external reputation services like Sender Score. They check blacklists. They consider authentication results. All of this feeds into a decision about how to handle your message.
A high Sender Score doesn't guarantee inbox placement—ISPs weigh many factors. But a low Sender Score almost guarantees problems. It's a necessary but not sufficient condition for good deliverability.
The correlation between Sender Score and inbox placement is well-documented. Senders with scores above 90 see inbox placement rates around 90%. Scores between 70-80 see rates around 70%. Below 70, deliverability drops sharply. These aren't guarantees, but they're strong patterns.
Checking your Sender Score
Validity provides free Sender Score lookups at senderscore.org. Enter your sending IP address, and you'll see your current score along with some diagnostic information.
If you're using an email service provider, you might be sending from shared IPs. In that case, the Sender Score reflects the collective behavior of everyone using those IPs, not just you. This is one argument for dedicated IPs if you're a high-volume sender—you control your own reputation.
For more detailed analysis, Validity offers paid tools that show historical trends, comparative benchmarks, and specific factors affecting your score. These can be valuable for diagnosing persistent problems.
Remember that Sender Score is IP-based. If you send from multiple IPs, each has its own score. If you've recently changed email providers or IPs, your new infrastructure might have a different score than your old one.
Factors that hurt your score
Understanding what damages Sender Score helps you avoid those behaviors.
Complaint rates are the biggest factor. When recipients click "Report Spam" or "Junk," that feedback reaches reputation systems. Even a 0.1% complaint rate—one complaint per thousand emails—can start affecting your score. Above 0.3%, you're in serious trouble.
Spam trap hits devastate scores. Sending to addresses that exist solely to catch spammers proves you're either using bad lists or not maintaining good hygiene. A few trap hits can drop your score dramatically.
High bounce rates indicate list quality problems. If you're sending to many addresses that don't exist, you're either not validating signups or not removing bounces. Either way, it suggests poor practices.
Inconsistent sending patterns raise flags. Spammers often send in bursts—high volume for a short period before they get blocked. Legitimate senders typically have more consistent patterns. Erratic volume can hurt your score even if the email itself is fine.
Blacklist appearances directly impact the score. If you're listed on major blacklists, your Sender Score reflects that. The score often drops before you even notice the listing.
Improving your score
Raising a low Sender Score requires addressing the underlying issues, not gaming the metric.
Reduce complaints by sending wanted email. This sounds obvious, but it's where most problems originate. Are you emailing people who actually signed up? Is your content relevant to them? Is unsubscribing easy? Every complaint avoided is reputation preserved.
Clean your list aggressively. Remove hard bounces immediately. Remove soft bounces after repeated failures. Sunset subscribers who haven't engaged in 6-12 months. Validate new addresses at signup. A smaller, cleaner list outperforms a larger, dirty one.
Send consistently. Establish a regular sending pattern and stick to it. If you normally send weekly, don't suddenly send daily. If you need to increase volume, do it gradually. Predictability builds trust.
Warm new IPs properly. If you're starting with a new IP address, don't immediately send at full volume. Start small with your most engaged recipients, then gradually increase. This builds reputation without triggering defensive responses.
Monitor and respond quickly. Check your Sender Score regularly. Watch for drops and investigate immediately. The faster you identify and fix problems, the less damage they cause.
The limitations of Sender Score
Sender Score is useful but not definitive. Understanding its limitations helps you use it appropriately.
It's IP-based, not domain-based. If you're building domain reputation (increasingly important), Sender Score doesn't directly measure that. You need other tools to assess domain reputation.
It's one company's metric. Validity calculates Sender Score based on their data and algorithms. ISPs have their own systems that might weight factors differently. A good Sender Score doesn't guarantee good reputation with every ISP.
It's retrospective. The score reflects past behavior, not current state. If you fixed a problem yesterday, the score won't reflect that immediately. Conversely, if you just caused a problem, the score might not show it yet.
It doesn't capture everything. Content quality, engagement rates, authentication—many factors affect deliverability that aren't directly reflected in Sender Score. A perfect score with terrible content still won't reach the inbox.
Beyond Sender Score
Sender Score is one tool in your deliverability toolkit. Complement it with other monitoring.
Google Postmaster Tools shows your reputation specifically with Gmail—often your largest recipient segment. It provides domain reputation, IP reputation, spam rates, and authentication success rates.
Microsoft SNDS offers similar insights for Outlook.com and related Microsoft properties. The interface is less polished but the data is valuable.
Your own metrics matter most. Track delivery rates, open rates, click rates, bounce rates, and complaint rates over time. These direct measurements tell you how your email is actually performing, regardless of what any reputation score says.
Feedback loops from major ISPs notify you when recipients mark your email as spam. This real-time data helps you identify problems before they tank your reputation scores.
Frequently asked questions
What's a good Sender Score?
Above 80 is generally good; above 90 is excellent. Between 70-80 is acceptable but leaves room for improvement. Below 70 indicates problems that need attention. Below 50 means serious deliverability issues.
How quickly does Sender Score change?
The score updates based on recent sending behavior, typically reflecting the past 30 days. Significant changes in behavior can move the score within a week or two. Recovery from major problems might take a month or more of consistent good behavior.
Does Sender Score matter if I use a shared IP?
Yes, but you have less control. The score reflects everyone using that IP. If your email provider maintains good practices and removes bad actors quickly, shared IP scores stay healthy. If not, you suffer for others' behavior.
Can I improve my Sender Score quickly?
Not really. The score reflects sustained behavior patterns. Quick fixes don't exist. You can stop the bleeding quickly by fixing acute problems, but rebuilding a damaged score takes weeks of consistent good practices.