Sender reputation is a score mailbox providers assign to your domain and IP address based on your sending behavior. Domain reputation follows your domain across all IPs and ESPs — it's the most important factor for Gmail. IP reputation is tied to specific sending IPs — more important for Outlook. Check domain reputation in Google Postmaster Tools (High/Medium/Low/Bad). Check IP reputation in Microsoft SNDS and Cisco Talos. Both must be healthy for reliable inbox placement.
Sender Reputation Explained: Domain vs IP Reputation
How Reputation Works
Every time you send email, the receiving server evaluates your trustworthiness. This evaluation creates a reputation score for both your sending domain and your sending IP address.
Good reputation → inbox. Bad reputation → spam (or rejection).
Domain Reputation
Your domain reputation is tied to the domain in your From: header. It persists across:
- Different ESPs
- Different IP addresses
- Different sending services
If you damage your domain reputation on Mailchimp and switch to Klaviyo, the reputation follows your domain. Switching providers doesn't reset domain reputation.
How to Check Domain Reputation
Google Postmaster Tools (most important):
- Go to postmaster.google.com
- Verify your domain
- View the Domain Reputation dashboard
- Rating scale: High (good) → Medium (watch) → Low (problem) → Bad (critical)
What Affects Domain Reputation
| Factor | Impact |
|---|---|
| Spam complaint rate | Highest — above 0.1% damages, above 0.3% is critical |
| Spam trap hits | High — pristine traps cause immediate damage |
| Bounce rate | Medium — above 5% indicates list quality problems |
| Engagement | Medium — low open/click rates signal unwanted mail |
| Authentication failures | Medium — SPF/DKIM/DMARC failures erode trust |
| Blacklisting | High — domain blacklists (URIBL, SURBL) are severe |
IP Reputation
IP reputation is tied to the IP address sending your email. On shared IPs, your reputation is shared with other senders. On dedicated IPs, it's yours alone.
How to Check IP Reputation
Microsoft SNDS (for Outlook):
- sendersupport.olc.protection.outlook.com/snds/
- Register your sending IPs → view complaint data, trap hits, filters
Cisco Talos Intelligence (general):
- talosintelligence.com/reputation_center
- Enter your IP → see reputation rating (Good/Neutral/Poor)
MXToolbox Blacklist Check:
- mxtoolbox.com/blacklists.aspx
- Enter IP → check against 70+ blacklists
Reputation Recovery
Mild Damage (Medium reputation, or recent small complaint spike)
- Send to most engaged recipients only (opened in last 30 days)
- Reduce volume by 50% for 2 weeks
- Monitor complaint rate — must stay below 0.05%
- Gradually restore volume as reputation improves
Severe Damage (Bad/Low reputation, blacklisted)
- Stop non-essential sending immediately
- Get delisted from any blacklists (see blacklist guide)
- Clean your entire list — remove all unengaged contacts (90+ days)
- Validate remaining list through ZeroBounce or NeverBounce
- Send only to your top 10% most engaged recipients
- Volume: start at 500-1,000/day maximum
- Monitor Postmaster Tools daily
- Gradually increase over 4-8 weeks as reputation rebuilds
- Implement sunset policy to prevent recurrence
Timeline
| Starting State | Target | Typical Duration |
|---|---|---|
| Medium → High | Restore to healthy | 2-3 weeks |
| Low → High | Full recovery | 4-6 weeks |
| Bad → High | Full recovery | 6-8+ weeks |
| Blacklisted → Clean | Depends on blacklist | 1 day to 2 weeks for delisting, then 4-8 weeks for reputation |
Practitioner note: The single most important reputation metric: spam complaint rate. Google tells you to stay below 0.3%. I tell clients to stay below 0.05%. The difference between 0.05% and 0.3% is the difference between "great deliverability" and "technically within tolerance but vulnerable." Leave margin.
Practitioner note: When a client's reputation is Bad, the first thing I do is segment their list by engagement. Often 20-30% of their list hasn't opened in 6+ months. Removing that segment and sending only to engaged contacts typically moves reputation from Bad to Medium within 2 weeks — before any other changes.
If your sender reputation has dropped and you need a recovery plan, schedule a consultation — I'll diagnose the exact cause and build a remediation timeline.
Sources
- Google: Postmaster Tools
- Microsoft: SNDS
- Cisco: Talos Intelligence
v1.0 · March 2026
Frequently Asked Questions
What's more important, domain or IP reputation?
Domain reputation, especially for Gmail (the largest mailbox provider). Gmail weights domain reputation more heavily than IP reputation. Outlook relies more on IP reputation. You need both, but fixing domain reputation is the higher priority.
How do I check my sender reputation?
Domain reputation: Google Postmaster Tools (free, shows High/Medium/Low/Bad for Gmail). IP reputation: Microsoft SNDS (free, for Outlook), Cisco Talos Intelligence (free lookup), MXToolbox (free, checks blacklists). Check all three for a complete picture.
What damages sender reputation?
High spam complaint rate (above 0.1%), hitting spam traps, high bounce rate (above 5%), landing on blacklists, sudden volume spikes, sending to unengaged recipients, and authentication failures.
How long does it take to repair reputation?
2-8 weeks depending on severity. Mild damage (Medium reputation): 2-3 weeks of clean sending to engaged recipients. Severe damage (Bad reputation): 4-8 weeks of dramatically reduced volume, aggressive list cleaning, and exclusive engagement with active subscribers.
Does switching ESPs reset my reputation?
Domain reputation: no, it follows your domain regardless of ESP. IP reputation: yes, new IPs start fresh (requires warmup). This is why ESP migration doesn't fix fundamental reputation problems — the domain carries the damage.
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