What is Sender Reputation?
Sender reputation is a score that mailbox providers (such as Gmail, Outlook, and Yahoo Mail) assign to every organization that sends email. It reflects how trustworthy and legitimate your email traffic is, based on your historical sending behavior, technical configuration, and recipient engagement.
A high sender reputation score means mailbox providers trust you and are more likely to deliver your messages directly to the inbox. A low sender reputation score means your emails may be filtered to spam, throttled, or rejected entirely.
How Mailbox Providers Evaluate Reputation
Every major mailbox provider uses its own algorithms to decide where to place incoming email. While the exact formulas are proprietary, the general approach is consistent across providers.
Google (Gmail)
Google evaluates sender reputation at both the domain level and the IP level. Gmail's Postmaster Tools provides data on domain reputation (High, Medium, Low, Bad) and IP reputation. Google places heavy emphasis on user engagement signals, spam complaints, and proper authentication (SPF, DKIM, DMARC). Domains with a DMARC policy of quarantine or reject tend to receive better treatment.
Microsoft (Outlook, Hotmail, Office 365)
Microsoft uses a system called Smart Network Data Services (SNDS) and maintains its own internal sender reputation system. Microsoft tends to weight IP reputation heavily and uses a combination of content filtering (SmartScreen), authentication checks, and feedback loop data from Junk Mail Reporting. Microsoft also participates in the Junk Email Reporting Partner Program (JMRP).
Yahoo Mail / AOL
Yahoo Mail uses a reputation system that considers sending volume consistency, complaint rates, bounce rates, and authentication. Yahoo was an early proponent of DKIM and heavily rewards domains that implement DMARC with a reject policy. Yahoo's Complaint Feedback Loop (CFL) provides senders with spam complaint data.
Key Factors That Affect Your Reputation
While each provider weighs factors differently, these are the core signals that affect your sender reputation across all major platforms.
1. Email Authentication
Proper configuration of SPF, DKIM, and DMARC is the foundation of sender reputation. These protocols prove that you are who you say you are and that your messages have not been tampered with in transit.
- SPF (Sender Policy Framework) - Specifies which servers are authorized to send email on behalf of your domain.
- DKIM (DomainKeys Identified Mail) - Adds a cryptographic signature to each message to verify it was not altered.
- DMARC (Domain-based Message Authentication, Reporting and Conformance) - Tells receiving servers what to do when SPF or DKIM fail, and enables reporting.
For a detailed walkthrough, see our Email Authentication Guide.
2. Sending Volume and Consistency
Sudden spikes in sending volume are a common spam indicator. Mailbox providers prefer senders who maintain consistent, predictable sending patterns. If you need to increase your sending volume, do so gradually over days or weeks (a process called "warming up").
3. Recipient Engagement
How recipients interact with your emails directly impacts your reputation. Positive signals include opens, clicks, replies, and moving messages from spam to inbox. Negative signals include deleting without reading, marking as spam, and ignoring messages entirely.
4. Spam Complaints
When a recipient clicks "Report Spam" or "Mark as Junk," that complaint is reported back to the sender's ESP through a feedback loop. A complaint rate above 0.1% (1 complaint per 1,000 emails) is generally considered problematic. Google recommends keeping complaints below 0.1% and warns that exceeding 0.3% will cause significant deliverability issues.
5. Bounce Rates
Sending to invalid email addresses (hard bounces) signals poor list hygiene and is a strong negative reputation factor. Keep your hard bounce rate below 2%. For more details, see our guide on Understanding Bounce Rates.
6. Blacklist Listings
If your domain or sending IP appears on one or more email blacklists, your reputation will suffer significantly. Blacklists are maintained by organizations like Spamhaus, Barracuda, and SORBS. Use our Blacklist Checker to see if you are listed.
7. Content Quality
While content filtering is less influential than it used to be, sending emails with spammy language, misleading subject lines, or excessive image-to-text ratios can still negatively impact deliverability. Always write clear, honest subject lines and provide valuable content.
IP Reputation vs Domain Reputation
Historically, email reputation was tied primarily to the sending IP address. If you sent email from a "clean" IP, your messages were more likely to be delivered. This is still partially true, but the industry has shifted significantly toward domain-based reputation.
| Factor | IP Reputation | Domain Reputation |
|---|---|---|
| What is tracked | The IP address of the sending server | The domain in the From address and DKIM signature |
| Portability | Tied to infrastructure; changes when you switch ESPs | Follows you regardless of what ESP or IP you use |
| Shared vs Dedicated | Shared IPs mean shared reputation with other senders | Always unique to your domain |
| Trend | Still relevant, but decreasing in relative weight | Increasingly the primary factor at major providers |
| Provider emphasis | Microsoft still weighs IP reputation heavily | Google prioritizes domain reputation |
For most senders today, domain reputation is the more important of the two. This is especially true if you use a shared IP through an ESP like Mailchimp, SendGrid, or Amazon SES, where your IP reputation is influenced by other senders on the same infrastructure.
When to Consider a Dedicated IP
A dedicated IP gives you full control over your IP reputation, since no other senders share it. Consider a dedicated IP if:
- You send more than 50,000 emails per month consistently
- You need maximum control over deliverability
- Your shared IP has been flagged due to other senders' behavior
- You send time-sensitive transactional email that must reach the inbox reliably
However, a dedicated IP also means you bear full responsibility for the reputation. You must warm it up properly and maintain consistent volume. For low-volume senders, a shared IP through a reputable ESP is often the better choice, as the ESP's overall sending practices keep the IP reputation healthy.
How to Check Your Sender Reputation
Because each mailbox provider maintains its own reputation data, there is no single "official" sender reputation score. However, several tools can help you understand your standing.
Our Sender Reputation Checker
Our free Sender Reputation Checker provides a comprehensive Sender Reputation Score that evaluates your authentication setup (SPF, DKIM, DMARC), blacklist status, DNS configuration, and mail server infrastructure. You receive an A-F grade with specific, actionable recommendations.
Google Postmaster Tools
If you send email to Gmail recipients, Google Postmaster Tools is essential. It shows your domain reputation, IP reputation, spam rate, authentication results, and delivery errors. You will need to verify domain ownership to access the data.
Microsoft SNDS
Microsoft's Smart Network Data Services shows how your IP addresses are performing when delivering to Outlook.com, Hotmail, and other Microsoft mail platforms. It provides complaint rate data and trap hit data for your sending IPs.
Building and Maintaining Good Reputation
Building a strong sender reputation takes time and consistent effort. Here are the most effective strategies.
Authenticate Everything
Set up SPF, DKIM, and DMARC for every domain you send email from. Use our free tools to verify your configuration:
Maintain Clean Lists
Remove hard bounces immediately. Prune inactive subscribers who have not engaged in 6-12 months. Use double opt-in for new signups to ensure valid, consented addresses. Never purchase email lists.
Send Consistently
Establish a regular sending cadence and stick to it. If you need to increase volume, ramp up gradually. Sudden spikes in volume look suspicious to mailbox providers.
Make Unsubscribing Easy
Every marketing email should include a visible, one-click unsubscribe link. It is better for someone to unsubscribe than to mark your email as spam. Support the List-Unsubscribe header for one-click unsubscribe in email clients.
Monitor Your Metrics
Track bounce rates, complaint rates, open rates, and deliverability metrics. Set up alerts for unusual changes. Use Google Postmaster Tools and Microsoft SNDS to monitor provider-specific data.
Warm Up New Domains and IPs
When you start sending from a new domain or IP, begin with a small volume of email to your most engaged recipients. Gradually increase volume over 2-4 weeks. This establishes a positive sending history before you reach full volume.
Understanding Reputation Signals in Detail
Mailbox providers use both positive and negative signals to compute your reputation. Understanding these signals helps you prioritize your efforts.
Positive Signals
- Proper authentication - Valid SPF, DKIM, and DMARC records with a policy of quarantine or reject
- Consistent sending patterns - Predictable volume and frequency over time
- High engagement - Recipients opening, clicking, and replying to your emails
- Low complaint rates - Minimal spam reports from recipients
- Low bounce rates - Very few invalid addresses in your sends
- Inbox moves - Recipients moving your messages from spam to inbox
- Contact list additions - Recipients adding your address to their contacts
- Forward and share actions - Recipients forwarding your emails to others
Negative Signals
- Spam complaints - Recipients clicking "Report Spam" or "Mark as Junk"
- Spam trap hits - Sending to addresses that are known spam traps
- High bounce rates - Sending to a significant number of invalid addresses
- Blacklist presence - Being listed on one or more email blacklists
- Sudden volume spikes - Dramatic increases in sending volume without gradual ramp-up
- Low engagement - High rates of deletion without reading
- Missing authentication - No SPF, DKIM, or DMARC records
- Purchased or scraped lists - Sending to people who never opted in
Common Misconceptions About Sender Reputation
"I can buy a good reputation by using a clean IP"
While a clean IP helps, modern mailbox providers increasingly rely on domain reputation. Your sending domain follows you regardless of which IP or ESP you use. Changing IPs without fixing the underlying behavior will not solve reputation problems.
"My emails are not spam, so reputation does not affect me"
Reputation applies to all senders, not just spammers. Legitimate senders with poor list hygiene, missing authentication, or inconsistent sending patterns can still develop a poor reputation. Even newsletters people signed up for can end up in spam if the sender's reputation declines.
"If my open rates are good, my reputation must be fine"
Open rate data can be misleading due to privacy features like Apple's Mail Privacy Protection, which pre-loads tracking pixels. Additionally, if many of your emails are going to spam, the recipients who do open represent only those whose filters happened to deliver your message. A falling delivery rate might mask itself as a stable or even improving open rate.
"One bad send will ruin my reputation forever"
Sender reputation is based on patterns over time, not individual events. While a single bad send can cause a temporary dip, consistently good behavior will recover your standing. The exception is severe events like hitting a major spam trap network or generating an extremely high complaint rate, which may require active remediation.
For more actionable strategies, read our full guide on Improving Email Deliverability.
Building Reputation for a New Domain
New domains have no reputation at all, which is often treated with suspicion by mailbox providers. Building reputation from scratch requires a careful, deliberate approach.
The Warmup Period
A new domain needs a "warmup" period where you gradually establish a positive sending history. This typically takes 2-4 weeks for moderate volumes, and up to 8 weeks for high-volume senders. During this time:
- Start by sending small batches (50-200 emails per day) to your most engaged subscribers
- Increase volume by 25-50% every 2-3 days, as long as metrics remain healthy
- Focus on recipients who are most likely to open and engage with your messages
- Monitor bounce rates, complaint rates, and inbox placement closely at each stage
Authentication Before Sending
Configure all authentication records (SPF, DKIM, DMARC) before sending your first email. Starting with proper authentication establishes a strong foundation from day one. A domain that begins sending without authentication will start accumulating negative reputation signals immediately.
Domain Age Matters
Mailbox providers consider domain age as a factor. Brand new domains (registered within the last 30 days) are treated with extra scrutiny because spammers frequently register new domains. If possible, register your sending domain well in advance of when you plan to start sending, and set up a basic website on it so it does not appear to be a throwaway domain.
Recovering From Reputation Damage
If your sender reputation has declined, recovery is possible but requires patience and consistent action.
Step 1: Diagnose the Problem
Use our Sender Reputation Checker and Blacklist Checker to assess your current standing. Review Google Postmaster Tools for Gmail-specific data. Identify the specific factors causing the decline.
Step 2: Fix Root Causes
Address whatever is causing the damage: clean your list, fix authentication, resolve blacklist listings, reduce complaints, or secure a compromised server. Recovery cannot begin until the root cause is eliminated.
Step 3: Reduce Volume Temporarily
Scale back to sending only to your most engaged subscribers. This generates positive engagement signals while you rebuild. A smaller list with high engagement is better for recovery than a large list with mixed engagement.
Step 4: Rebuild Gradually
As metrics improve, gradually expand your sending volume and audience. This process is similar to warming up a new domain. Monitor at each stage and slow down if you see any negative trends.
Recovery timelines vary. Minor reputation dips may resolve in 1-2 weeks of clean sending. Major damage (blacklisting, sustained high complaint rates) can take 4-8 weeks or longer to fully recover from.