IP Reputation Monitoring: How to Track

IP Reputation vs Domain Reputation

Modern deliverability depends on both IP and domain reputation, but their roles differ:

IP reputation: The sending server's history. ISPs track complaint rates, spam trap hits, and sending patterns per IP address.

Domain reputation: Your domain's history across all IPs. Follows you when you change ESPs or IPs.

For dedicated IP users, IP reputation is critical. For shared IP users, domain reputation matters more because you can't control the IP's history.

Free IP Reputation Tools

Sender Score (Validity)

The most widely referenced IP reputation metric.

URL: senderscore.org

What it shows:

• Score 0-100 for your sending IPs
• 30-day rolling average
• Complaint rate indicators
• Blacklist status

Score interpretation:

Score	Rating	Action
90-100	Excellent	Maintain current practices
80-89	Good	Monitor for changes
70-79	Fair	Investigate and improve
50-69	Poor	Significant issues to address
Below 50	Bad	Major deliverability problems

Limitations: Updates daily, not real-time. May not have data for low-volume IPs.

Google Postmaster Tools

Gmail-specific reputation for your sending infrastructure.

URL: postmaster.google.com

What it shows:

• IP Reputation: High/Medium/Low/Bad
• Domain Reputation: High/Medium/Low/Bad
• Spam rate percentage
• Authentication success rates

IP reputation ratings:

• High: Good standing, inbox placement expected
• Medium: Some issues, may see spam folder placement
• Low: Problems detected, likely hitting spam
• Bad: Severe issues, most mail rejected or spammed

See our Google Postmaster Tools guide for detailed setup.

Microsoft SNDS

Outlook/Hotmail reputation data.

URL: sendersupport.olc.protection.outlook.com/snds

What it shows:

• IP activity status (Green/Yellow/Red)
• Complaint percentage
• Spam trap hits
• Filter result data

Setup: Requires IP ownership verification. Not available for shared IPs you don't control.

See our Microsoft SNDS guide for detailed setup.

Talos Intelligence (Cisco)

Cisco's email security intelligence.

URL: talosintelligence.com

What it shows:

• Email reputation: Good/Neutral/Poor
• Web reputation (if applicable)
• Volume statistics
• Blacklist status

Useful for: Identifying issues with corporate email filters that use Cisco technology.

Barracuda Central

Barracuda's reputation lookup.

URL: barracudacentral.org/lookups

What it shows:

• IP reputation status
• Blacklist status
• Removal request links if listed

Useful for: Troubleshooting delivery to organizations using Barracuda spam filters.

What Affects IP Reputation

Positive Factors

• Low complaint rate: Below 0.1%
• Good engagement: Opens, clicks, replies
• Clean list: No spam traps, valid addresses
• Consistent volume: Gradual increases, no spikes
• Authentication: SPF, DKIM, DMARC passing

Negative Factors

• High complaints: Above 0.3% triggers problems
• Spam trap hits: Pristine or recycled traps
• Blacklist appearances: Major lists hurt immediately
• Volume spikes: Sudden increases trigger scrutiny
• Bounces: High hard bounce rate signals list issues
• No engagement: Sending to dead addresses

Practitioner note: The fastest way to destroy IP reputation is a sudden volume spike followed by high complaints. I've seen new IPs go from good to blocklisted in 48 hours from one bad campaign.

Monitoring Schedule

For Dedicated IP Users

Frequency	Tool	Purpose
Daily	ESP dashboard	Bounce/complaint rates
Weekly	Sender Score	Overall reputation trend
Weekly	Google Postmaster	Gmail-specific reputation
Weekly	SNDS	Outlook-specific data
After issues	All tools	Diagnose problems

For Shared IP Users

Focus on domain reputation instead—you can't control shared IP reputation directly. Monitor:

• Domain reputation via Postmaster Tools
• ESP-reported deliverability metrics
• If problems persist, consider dedicated IPs

Interpreting Reputation Data

Declining Scores

If Sender Score drops 10+ points:

1. Check recent campaigns for complaints
2. Look for blacklist appearances
3. Review list imports or changes
4. Check for authentication failures

"Bad" Rating in Postmaster Tools

Gmail "Bad" IP reputation means:

1. Stop marketing campaigns immediately
2. Continue transactional email only
3. Investigate root cause
4. See IP reputation crashed for recovery steps

Conflicting Data Across Tools

Different tools may show different ratings. Trust:

• Postmaster Tools for Gmail issues
• SNDS for Outlook issues
• Sender Score for general trends
• Your ESP data for aggregate delivery rates

Dedicated IP Best Practices

If you're using dedicated IPs:

Warming

New IPs have no reputation. Build it gradually:

1. Start with 50-200 emails/day
2. Increase 20-50% daily when metrics are clean
3. Full warmup takes 4-8 weeks

See our IP warmup schedule.

Maintaining Reputation

• Send consistently (not huge spikes then silence)
• Monitor complaint rates per campaign
• Remove unengaged subscribers
• Never buy or rent lists
• Process bounces immediately

Recovery

If reputation crashes:

1. Identify and stop the problem source
2. Reduce volume to engaged subscribers only
3. Send valuable content (not promotional)
4. Rebuild slowly over 4-8 weeks
5. Consider new IP if damage is severe

When to Investigate

Check IP reputation immediately when:

• Bounce rates spike above 5%
• Spam complaints exceed 0.3%
• Open rates drop 20%+ suddenly
• ESP reports deliverability warnings
• Recipients report missing emails

If your IP reputation has dropped and you're not sure how to recover, or you need help building a monitoring routine that catches problems early, schedule a consultation to diagnose the issue and create a recovery plan.

Sources

• Validity: Sender Score
• Google: Postmaster Tools
• Microsoft: SNDS
• Cisco: Talos Intelligence

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v1.0 · March 2026