IP and Domain Reputation: The Hidden Factor in Email Deliverability
Understand how IP and domain reputation affects email delivery. Monitor reputation, identify blacklisting, and implement practices that protect sender credibility.
Your email infrastructure can be technically perfect-SPF, DKIM, DMARC all passing-and emails still land in spam or get rejected. The missing piece is reputation: the trust score that mailbox providers assign to your sending IPs and domains based on historical behavior.
Reputation is earned over time and destroyed in moments. A compromised account sending spam, a misconfigured application blasting emails, or even aggressive marketing practices can tank your reputation overnight. This guide covers how reputation works, how to monitor it, and how to recover when things go wrong.
How Reputation Works
Mailbox providers (Gmail, Microsoft, Yahoo) maintain reputation scores for every IP address and domain that sends them email. These scores determine whether your messages reach the inbox, land in spam, or get rejected outright.
┌─────────────────────────────────────────────────────────────────────────┐
│ REPUTATION SCORING MODEL │
├─────────────────────────────────────────────────────────────────────────┤
│ │
│ POSITIVE SIGNALS NEGATIVE SIGNALS │
│ ──────────────── ──────────────── │
│ │
│ ✓ Low bounce rates ✗ High bounce rates │
│ ✓ Low spam complaints ✗ Spam complaints │
│ ✓ High engagement (opens/clicks) ✗ Spam trap hits │
│ ✓ Consistent sending volume ✗ Sudden volume spikes │
│ ✓ Clean list hygiene ✗ Blacklist appearances │
│ ✓ Authentication (SPF/DKIM/DMARC) ✗ Authentication failures │
│ ✓ Proper unsubscribe handling ✗ High unsubscribe rates │
│ │
│ ═══════════════════════════════════════════════════════════════════ │
│ │
│ REPUTATION SCORE │
│ ──────────────── │
│ │
│ 90-100 ████████████████████████████████████ EXCELLENT │
│ → Priority inbox placement │
│ │
│ 70-89 ██████████████████████████ GOOD │
│ → Normal inbox delivery │
│ │
│ 50-69 ████████████████ NEUTRAL │
│ → Some spam folder placement │
│ │
│ 25-49 ████████ POOR │
│ → Significant spam filtering │
│ │
│ 0-24 ████ BAD │
│ → Rejections, blocking │
│ │
└─────────────────────────────────────────────────────────────────────────┘
IP Reputation vs Domain Reputation
Both matter, but they work differently:
| Factor | IP Reputation | Domain Reputation |
|---|---|---|
| What it tracks | Sending server IP address | Your domain (From, DKIM) |
| Persistence | Tied to IP; changes if you move | Follows your domain everywhere |
| Shared vs Dedicated | Often shared on ESP platforms | Always specific to your domain |
| Recovery time | Days to weeks | Weeks to months |
| Primary use | Connection-level filtering | Content-level filtering |
IP reputation matters most for connection-level decisions: will the receiving server even accept the connection? Low IP reputation results in connection timeouts, rate limiting, or outright blocks.
Domain reputation influences content-level decisions: once accepted, does the message go to inbox or spam? Domain reputation increasingly dominates because senders can change IPs but not domains.
Monitoring Your Reputation
Don't wait for delivery problems to discover reputation issues. Proactive monitoring catches problems early.
Google Postmaster Tools
Google Postmaster Tools provides direct visibility into how Gmail views your domain:
┌─────────────────────────────────────────────────────────────────────────┐
│ GOOGLE POSTMASTER TOOLS DASHBOARD │
├─────────────────────────────────────────────────────────────────────────┤
│ │
│ Domain Reputation IP Reputation Spam Rate │
│ ───────────────── ───────────── ───────── │
│ HIGH MEDIUM 0.3% │
│ ┌────────────┐ ┌────────────┐ ┌────────────┐ │
│ │ ██████████ │ │ ██████░░░░ │ │ █░░░░░░░░░ │ │
│ │ ██████████ │ │ ██████░░░░ │ │ █░░░░░░░░░ │ │
│ └────────────┘ └────────────┘ └────────────┘ │
│ │
│ Authentication Success │
│ ────────────────────── │
│ SPF: 99.8% ████████████████████████████████████████ │
│ DKIM: 99.9% ████████████████████████████████████████ │
│ DMARC: 99.7% ███████████████████████████████████████░ │
│ │
│ Encryption │
│ ────────── │
│ TLS: 100% ████████████████████████████████████████ │
│ │
└─────────────────────────────────────────────────────────────────────────┘
Setup:
- Go to postmaster.google.com
- Add and verify your domain (DNS TXT record)
- Monitor daily once you have sufficient volume (100+ emails/day to Gmail)
Microsoft SNDS
Microsoft Smart Network Data Services provides similar insights for Outlook/Hotmail:
- Visit sendersupport.olc.protection.outlook.com/snds
- Request access for your IP ranges
- Monitor spam complaints and trap hits
Third-Party Reputation Services
| Service | What It Measures | Cost |
|---|---|---|
| Sender Score (Validity) | IP reputation 0-100 | Free |
| Talos Intelligence (Cisco) | IP/domain reputation | Free |
| Barracuda Central | IP reputation | Free |
| MXToolbox | Blacklist monitoring | Freemium |
| 250ok / Validity | Comprehensive reputation | Paid |
Sender Score (senderscore.org) provides a 0-100 score for any IP address. Scores above 80 generally indicate good reputation.
# Quick reputation check
curl -s "https://www.senderscore.org/lookup.php?lookup=YOUR_IP"
Blacklists: Detection and Removal
Blacklists (DNSBLs) are real-time databases of IPs known to send spam. Major providers check these lists when receiving email.
Major Blacklists
| Blacklist | Impact | Removal |
|---|---|---|
| Spamhaus (SBL, XBL, PBL) | Severe | Manual request |
| Barracuda | Significant | Automatic after 12hrs |
| SpamCop | Moderate | Automatic decay |
| SORBS | Moderate | Manual request |
| CBL (Composite) | Moderate | Automatic after cleanup |
| URIBL / SURBL | Domain blacklists | Manual request |
Checking Blacklist Status
# Check if IP is on Spamhaus
dig +short 4.3.2.1.zen.spamhaus.org
# Response of 127.0.0.x means listed
# No response means clean
# Multi-blacklist check
# Use MXToolbox: mxtoolbox.com/blacklists.aspx
Blacklist Removal Process
┌─────────────────────────────────────────────────────────────────────────┐
│ BLACKLIST REMOVAL WORKFLOW │
├─────────────────────────────────────────────────────────────────────────┤
│ │
│ 1. IDENTIFY THE CAUSE │
│ ──────────────────── │
│ • Review mail logs for unusual activity │
│ • Check for compromised accounts │
│ • Audit application sending behavior │
│ • Identify spam trap hits │
│ │
│ 2. FIX THE UNDERLYING ISSUE │
│ ─────────────────────── │
│ • Secure compromised accounts │
│ • Fix application bugs │
│ • Clean mailing lists │
│ • Implement rate limiting │
│ │
│ 3. REQUEST REMOVAL │
│ ──────────────────── │
│ • Spamhaus: spamhaus.org/lookup │
│ • Barracuda: barracudacentral.org/lookups │
│ • SpamCop: spamcop.net/bl.shtml │
│ │
│ 4. MONITOR FOR RE-LISTING │
│ ──────────────────────── │
│ • Set up automated blacklist monitoring │
│ • Alert on new listings │
│ • Investigate immediately if re-listed │
│ │
│ ⚠️ WARNING: Requesting removal without fixing the cause │
│ results in immediate re-listing │
│ │
└─────────────────────────────────────────────────────────────────────────┘
Common Reputation Killers
Spam Traps
Spam traps are email addresses that should never receive legitimate email. Hitting them signals poor list hygiene.
| Trap Type | Description | How to Avoid |
|---|---|---|
| Pristine | Addresses that never opted in | Never purchase lists |
| Recycled | Abandoned addresses repurposed | Regular list cleaning |
| Typo | Common typo domains (gmial.com) | Email validation at signup |
Purchased Lists
Purchasing email lists is the fastest path to reputation destruction. These lists contain:
- Spam traps planted to catch purchasers
- Outdated addresses that bounce
- People who never consented
One campaign to a purchased list can blacklist your IP and damage your domain reputation for months.
Volume Spikes
Mailbox providers notice sudden volume changes. A domain that sends 100 emails/day suddenly sending 10,000 triggers spam filtering.
┌─────────────────────────────────────────────────────────────────────────┐
│ VOLUME PATTERNS │
├─────────────────────────────────────────────────────────────────────────┤
│ │
│ SUSPICIOUS PATTERN HEALTHY PATTERN │
│ ───────────────── ─────────────── │
│ │
│ Volume Volume │
│ │ │ │
│ │ ▲ │ ▄▄▄ │
│ │ ███ │ ▄▄██████ │
│ │ ███ │ ▄▄████████ │
│ │ ███ │ ▄▄██████████ │
│ │ ███ │ ▄▄████████████ │
│ │ ▄▄▄ ███ ▄▄▄ │ ▄████████████████ │
│ └─────────────────► Time └───────────────────► Time │
│ │
│ Spike triggers filtering Gradual warmup builds trust │
│ │
└─────────────────────────────────────────────────────────────────────────┘
Complaint Rates
When recipients click "Report Spam," mailbox providers track this. High complaint rates destroy reputation:
| Complaint Rate | Impact |
|---|---|
| < 0.1% | Healthy |
| 0.1% - 0.3% | Warning zone |
| 0.3% - 0.5% | Reputation damage |
| > 0.5% | Severe filtering/blocking |
Gmail considers > 0.3% problematic. Even legitimate senders exceed this if they mail disengaged subscribers.
Building and Protecting Reputation
IP Warming
New IPs have no reputation-they're unknown entities. Warming gradually builds positive history:
┌─────────────────────────────────────────────────────────────────────────┐
│ IP WARMING SCHEDULE │
├─────────────────────────────────────────────────────────────────────────┤
│ │
│ Day Volume/Day Target Recipients │
│ ─── ────────── ───────────────── │
│ 1-2 50 Most engaged subscribers only │
│ 3-4 100 High engagement │
│ 5-7 250 High engagement │
│ 8-10 500 High + medium engagement │
│ 11-14 1,000 Medium engagement │
│ 15-21 2,500 Medium engagement │
│ 22-28 5,000 Broader audience │
│ 29-35 10,000 Full list minus inactives │
│ 36+ Scale up 25%/week as reputation builds │
│ │
│ ⚠️ IMPORTANT: │
│ • Only send to opt-in recipients during warmup │
│ • Monitor bounces and complaints closely │
│ • Slow down if you see deliverability issues │
│ • Warmup separately for each major provider │
│ │
└─────────────────────────────────────────────────────────────────────────┘
List Hygiene
Clean lists regularly to maintain reputation:
- Remove hard bounces immediately: Invalid addresses hurt reputation
- Suppress complaints: Never email anyone who complained
- Sunset inactive subscribers: Users who don't engage for 6-12 months hurt metrics
- Validate at signup: Block typos and fake addresses
Authentication Hygiene
Authentication failures damage domain reputation:
# Monitor DMARC reports for authentication issues
# Example aggregate report summary:
Source IP SPF DKIM DMARC Count
─────────────────────────────────────────────
192.0.2.1 pass pass pass 15,234
192.0.2.2 fail pass pass 1,203
198.51.100.5 fail fail fail 847 ← Unknown sender!
203.0.113.99 pass fail fail 423 ← DKIM broken
Investigate and fix all authentication failures. The fail/fail/fail entries are either spoofing attempts or misconfigured legitimate senders-both need attention.
Reputation Recovery
When reputation tanks, recovery takes time and discipline.
Immediate Actions
- Stop all non-essential sending: Reduce volume to minimum
- Identify the cause: Logs, DMARC reports, blacklist notices
- Fix the root cause: Before any recovery can begin
- Clean your list: Remove bounces, complaints, inactives
Recovery Timeline
| Reputation Level | Expected Recovery Time |
|---|---|
| Minor dip (70-80) | 1-2 weeks |
| Moderate damage (50-69) | 2-4 weeks |
| Severe damage (25-49) | 1-3 months |
| Blacklisted (< 25) | 3-6 months |
Recovery Strategy
┌─────────────────────────────────────────────────────────────────────────┐
│ REPUTATION RECOVERY PLAN │
├─────────────────────────────────────────────────────────────────────────┤
│ │
│ PHASE 1: STABILIZATION (Week 1-2) │
│ ───────────────────────────────── │
│ • Reduce sending volume by 80% │
│ • Send only to most engaged users │
│ • Monitor all metrics closely │
│ • Request blacklist removals (if applicable) │
│ │
│ PHASE 2: CLEANUP (Week 3-4) │
│ ────────────────────────── │
│ • Audit and clean entire list │
│ • Fix all authentication issues │
│ • Review and fix sending applications │
│ • Implement better monitoring │
│ │
│ PHASE 3: REBUILDING (Week 5+) │
│ ───────────────────────────── │
│ • Gradually increase volume (10-20%/week) │
│ • Continue monitoring metrics │
│ • Adjust based on deliverability │
│ • Full recovery when metrics stabilize │
│ │
└─────────────────────────────────────────────────────────────────────────┘
Reputation Monitoring Checklist
Set up ongoing monitoring before problems occur:
| Check | Frequency | Tool |
|---|---|---|
| Blacklist status | Daily | MXToolbox, automated |
| Google Postmaster | Daily | Postmaster Tools |
| Microsoft SNDS | Daily | SNDS Dashboard |
| Sender Score | Weekly | senderscore.org |
| Bounce rates | Per campaign | ESP dashboard |
| Complaint rates | Per campaign | ESP + feedback loops |
| DMARC reports | Weekly | DMARC analyzer |
Next Steps
Reputation management is ongoing. Build monitoring before you have problems, maintain clean lists, authenticate everything, and respond quickly to issues.
We help organizations monitor and recover email reputation. Request an assessment to evaluate your current sending reputation and identify risks.
Dealing with deliverability problems or blacklisting? We've recovered reputation for organizations facing severe blacklisting and helped rebuild sending infrastructure from scratch. Contact us for immediate assistance.