How to Fix Sender Reputation and Reach the Inbox Again

✨ Key takeaways

⭐ Your sender reputation determines whether emails reach inboxes or go to spam.

⭐ IP and domain reputation are influenced by complaints, bounces, engagement, and list quality.

⭐ A poor reputation harms deliverability, open rates, and campaign ROI.

⭐ Your reputation can be checked using specialized tools.

⭐ Consistent authentication, smart segmentation, and monitoring are essential for maintaining a good reputation.

⭐ Common myths—like relying solely on ESPs or focusing only on open rates—can lead to repeated mistakes.

There’s a certain irony in the way digital communication has evolved. In the early days of email, the biggest challenge was connection itself, like chunky interfaces and limited inbox capabilities. Today, we can send billions of messages in the blink of an eye, but the challenge has changed. Today it is not about whether an email can be sent, but whether it will ever reach its destination. And here we talk about sender reputation.

Much like a credit score governs access to financial systems, sender reputation determines whether your emails will be welcomed into inboxes or rerouted to spam purgatory. And like credit scores, most people don’t realize how fragile this reputation is until it’s already damaged. The good news is—sender reputation is not permanent. It can be rebuilt. 

This article will guide you through exactly that: understanding what sender reputation is, why it matters, how to check it, and—most importantly—how to fix sender reputation when things go wrong.

What Is Sender Reputation? 

Sender reputation is a score that email service providers (ESPs) and internet service providers (ISPs) assign to you as a sender. They are basically judging whether you’re a trustworthy communicator or a potential spammer. It’s calculated based on a mix of behavioral signals, technical infrastructure, and historical performance. 

There are two distinct yet interconnected layers to sender reputation: IP reputation and domain reputation. 

👉 IP reputation reflects the trustworthiness of the specific server (IP address) you’re sending from. If that IP has a history of sending unsolicited or low-quality emails, it’s likely to be flagged by receiving servers, reducing your deliverability. Besides, 55% of users mark unsolicited emails as spam.

👉 Domain reputation, on the other hand, is tied to your email domain (e.g., yourcompany.com). It assesses the long-term behavior of your domain across all campaigns, including engagement rates, complaint frequency, and compliance with authentication protocols. 

These two often influence each other, but not always in the same way. While IP reputation was historically more dominant, domain reputation has grown in importance as email systems have evolved to better track sender identity across different platforms and devices. 

 Why Sender Reputation Matters 

If sender reputation sounds like an abstract technical metric, we can make it more concrete: your reputation determines whether your emails are placed in the inbox, end up in spam, or are blocked altogether. While being placed in a spam folder is frustrating enough, the implications are even more serious.

Poor sender reputation can negatively affect your open and click-through rates and drastically reduce ROI on email campaigns. The trick of sender reputation is that it is often invisible: you might attribute a drop in engagement to bad timing or weak copy, while in fact your audience never even got the message. According to Validity’s 2023 Email Deliverability Benchmark Report, even 1 in 6 fully legitimate messages doesn’t reach recipients’ inboxes. 

Reputation doesn’t just influence deliverability alone—it affects your broader marketing ecosystem. If customers stop receiving transactional emails like confirmations or receipts, it will soon start to undermine their trust. If prospects don’t see your welcome emails, it disrupts your onboarding flow. Over time, a damaged sender reputation can ripple across channels, harming not just email marketing performance but also customer relationships and brand credibility.

Key Factors That Influence Sender Reputation 

🔷 Spam complaints

Every time a recipient clicks Mark as spam, it signals to mailbox providers that your content is unwanted. Even a small percentage of complaints (as little as 0.1%) can raise red flags. These reports feed directly into reputation algorithms, causing ISPs to restrict or block your future emails. The harsh reality is, it doesn’t matter if your email was technically “compliant”—if people don’t want it, you’re still penalized. Plus, 80% of users mark emails as spam simply if they look like spam. 

🔷 Bounce rates (hard and soft)

Bounces, especially hard ones, are another critical signal. Hard bounces happen when you send to an invalid or non-existent email address. Soft bounces occur when the recipient’s inbox is full or the server is temporarily unavailable. A high bounce rate suggests poor list hygiene, and providers may interpret this as a sign that you are spamming or buying lists.

🔷 Email engagement (opens, clicks, unsubscribes)

Mailbox providers track how people interact with your emails. If they’re opening, clicking, replying, or moving your emails to folders—great, that tells algorithms you’re welcome. But if users consistently delete without reading or unsubscribe massively, it leads to low sender reputation. 

🔷 Blacklist status

Major blacklists like Spamhaus or Barracuda can cause your emails to be blocked outright across entire networks. You could end up there for sending to spam traps, using shady acquisition tactics, or having your IP compromised by malware. Once listed, recovery is possible but complicated and not instant.

🔷 Volume and frequency consistency

ISPs watch how often you send and how much. A sudden spike in volume—say, going from 1,000 emails a day to 100,000—can look suspicious, especially if there’s no prior engagement history to back it up. So, grow your sending volumes slowly and consistently.

🔷 Use of authenticated protocols (SPF, DKIM, DMARC)

Without proper authentication, your emails will be easily forged and rejected. SPF, DKIM, and DMARC protocols help verify that you are who you say you are. These protocols prevent phishing, reduce spoofing, and show ISPs that you’re a legitimate sender. 

🔷 IP warming (if using a new IP)

When you switch to a new IP, you’re starting anew, which means mailbox providers know nothing about you. That is why sending full-volume campaigns right will most likely trigger red flags. So, warm up your IP gradually and slowly increase your sending volume to establish trust. 

How to Check Your Sender Reputation

If you are wondering how to check email sender reputation—you are asking the right question. Because, while there are clear signs of your sender reputation health, it is not something you should leave to a guess. Using some specialized tools instead is a much smarter choice. 

Tools and services:

Google Postmaster Tools

Developed to offer visibility into Gmail deliverability, Postmaster Tools presents data on spam rate, domain reputation, and authentication alignment. It is especially relevant given Gmail’s global dominance, and while its dashboard is intentionally minimalist, it provides one of the clearest lenses into how Gmail perceives your sending behavior. Marketers often treat this tool as the starting point for reputation triage.

Microsoft SNDS (Smart Network Data Services)

Unlike Gmail’s dashboard, SNDS offers a more detailed view—particularly useful for those reaching Outlook and Hotmail users. You can examine data related to complaint rates, spam trap hits, and message volumes mapped over time. Although the user interface can feel slightly outdated, the insight it offers is foundational, particularly for B2B campaigns where Microsoft domains are prominent.

SenderScore by Validity

SenderScore provides a numerical rating from 0 to 100—much like a credit score—for your IP’s sender behavior. This makes it especially helpful for benchmarking, as you can compare your score against industry averages. A sudden drop often correlates with deliverability issues, while consistent scores above 80 generally signal reliable performance. The platform is widely used in both diagnostics and presentations, serving as an external proof point in deliverability audits.

Talos Intelligence (Cisco)

Talos, operated by Cisco, is perhaps the most security-anchored tool on the list. It provides information about sender reputation through the lens of threat intelligence—flagging potential spammy behavior, blacklisting, or associations with malicious content. For marketers, it’s especially helpful in diagnosing why a particular IP or domain is blocked outright by certain filters. It’s also a reminder that email marketing is monitored within broader cybersecurity ecosystems.

What to look for in these dashboards 

Even though each platform offers a slightly different perspective, there are some shared patterns to look for in all of them. What you should look for goes beyond just sender reputation score because trends matter more than single data points. A spike in complaints, a sudden drop in reputation, or a dip in engagement metrics over time tells a more accurate story than one static number, and these tools help you track those movements.

Consistency is more important than a standalone number. If one tool shows a healthy sender reputation but another flags spam traps or engagement declines, don’t assume the best-case scenario. Instead, consider the differences in how mailbox providers assess risk. Gmail might forgive a soft bounce, while Outlook might tighten delivery thresholds. The more you monitor across systems, the clearer your sender reputation landscape becomes.

How to Recover a Damaged Sender Reputation 

✅ Identify the cause (high complaints, blacklist, etc.)

You can’t fix what you don’t understand. Start by analyzing your recent campaigns and sender health metrics—look at complaint rates, bounce logs, engagement drops, and blacklist listings. Often, a single campaign sent to the wrong segment or from a new IP without warning can trigger a whole downward spiral. Isolate the moment the decline began and trace it back to the root cause.

✅ Pause and clean up your list

If your reputation has already taken a hit, just continuing to send might even make things worse. Take a step back and scrub your list. Remove inactive subscribers, invalid emails, and any address that hasn’t shown engagement in months. Sending fewer emails to genuinely interested people is far more valuable than targeting lots of people who do not care.

✅ Implement re-engagement campaigns

Before cutting off low-engagement subscribers entirely, give them a chance to opt back in. Re-engagement emails—often called “we miss you” or “still interested?” campaigns—can help filter out the truly inactive from those who just need a nudge. Make it worth their time with a fresh offer, a quick update, or simply a reminder of why they signed up in the first place.

✅ Warm up your IP/domain again (if necessary)

If you’ve switched ESPs, started using a new IP, or were recently blacklisted, you may need to restart the warming process. This means gradually ramping up send volume and prioritizing your most active, engaged users first. It’s a slow but necessary rebuild to regain trust from inbox providers.

✅ Monitor improvements

Reputation recovery requires ongoing observation. It is important to track key metrics like inbox placement, complaint rates, and engagement levels on a constant basis. And never get too comfortable with your sender reputation, as it is very dynamic and requires constant vigilance.

Common Myths About Sender Reputation 

“If I buy a list once, it’s no big deal.”

This is perhaps the most damaging misconception. Purchased lists often contain outdated or invalid addresses, and worse, spam traps. Even a single campaign sent to a low-quality list can trigger a spike in complaints or blacklistings. 

“My ESP takes care of everything.”

While it’s true that reputable email service providers offer infrastructure and compliance tools, they cannot save your reputation from poor sending practices. If you send irrelevant content too frequently or ignore bounces and unsubscribes, the damage is yours to own, not theirs to fix.

“Sender Score and sender reputation are the same.”

Not quite. Sender Score (by Validity) is a public metric, useful for general benchmarking. Sender reputation, however, is calculated individually by each mailbox provider (like Gmail or Outlook) using their own criteria. So, while a low Sender Score often correlates with poor reputation, the two are not interchangeable. 

“If my open rates are decent, my sender reputation must be fine.”

Not necessarily. Open rates can be misleading—especially with Apple Mail’s privacy changes inflating metrics. Reputation depends on deeper signals like complaint rates, engagement over time, and bounce handling.

“Once fixed, sender reputation stays fixed.”

Unfortunately, no. Sender reputation is dynamic—it can degrade again if you slip back into bad habits. So, sender reputation check is something that requires consistent efforts.

To Sum Up

If you are wondering how to improve sender reputation, the answer lies not in purchased email lists, but in a consistent commitment to quality: authenticate your domain, send to people who want to hear from you, monitor your performance, and act at the first signs of decay. There’s no single fix—only a consistent, attentive practice.

And if you’ve looked at a bounce report or a declining open rate and asked yourself, “What happened to my email reputation?”—know this: reputations can be rebuilt. And the very act of asking that question means you’ve already begun.