What Is Sender Reputation?

By Braedon·Mailflow Authority·definitions

Reputation Is Everything

Sender reputation is the single biggest factor in whether your emails reach the inbox. It's not a single number — it's a composite assessment that mailbox providers calculate based on your historical sending behavior.

Think of it like a credit score for email. Good behavior builds it up. Bad behavior tears it down. And once it's damaged, recovery takes weeks of consistent good practices.

Two Types of Reputation

Domain Reputation

Tied to your sending domain (From: address). Follows you regardless of which ESP or IP you use. Gmail weights domain reputation heavily — switching ESPs won't fix a domain reputation problem.

IP Reputation

Tied to the IP address sending your email. On a dedicated IP, it's entirely your reputation. On a shared IP, other senders affect your reputation too.

What Builds Reputation

Low spam complaint rate (below 0.1%)
Low bounce rate (below 2%)
High engagement (recipients open, click, reply)
Consistent sending volume (no sudden spikes)
Clean authentication (SPF, DKIM, DMARC all passing)
No spam trap hits
No blacklist appearances

What Destroys Reputation

Spam complaints above 0.1% (Gmail's threshold)
Hitting spam traps (recycled or pristine)
Purchased or scraped lists
Sudden volume spikes
Sending to unengaged recipients for months
Authentication failures
Blacklist appearances

Practitioner note: The most common reputation killer I see isn't malicious behavior — it's neglect. A company sends to the same list for two years without removing unengaged recipients. Slowly, opens decline, complaints creep up, and one day Gmail quietly moves them to spam. By the time they notice, reputation is Bad.

Practitioner note: When clients migrate ESPs and their reputation "magically improves," it's usually because the new ESP's shared IP pool has good reputation — not because anything changed about their sending practices. The underlying problems will catch up within weeks.

For a complete guide, read sender reputation explained. To monitor reputation, set up Google Postmaster Tools.

If your reputation has crashed, schedule a consultation — I'll diagnose the root cause and build a recovery plan.

Sources

v1.0 · April 2026

Frequently Asked Questions

How is sender reputation calculated?

Mailbox providers weigh multiple signals: spam complaint rate (must stay below 0.1% for Gmail), bounce rate, spam trap hits, recipient engagement (opens, clicks, replies), volume consistency, and authentication pass rates. Each provider uses its own algorithm and weighting.

How do I check my sender reputation?

Google Postmaster Tools shows domain reputation for Gmail (High/Medium/Low/Bad). Microsoft SNDS shows IP reputation for Outlook. Sender Score by Validity provides a 0-100 score based on multiple signals. Check all three for a complete picture.

What's the difference between domain reputation and IP reputation?

Domain reputation follows your sending domain regardless of which IP sends the email. IP reputation is tied to specific sending IPs. Modern providers (especially Gmail) weight domain reputation more heavily. Both matter, but domain reputation is harder to escape.

How long does it take to rebuild sender reputation?

Typically 2-8 weeks of consistently good sending practices: low complaint rate, clean lists, engaged recipients, proper authentication. There's no shortcut — you earn reputation back through behavior.

Can I start fresh with a new domain?

Technically yes, but a new domain has zero reputation, which often performs worse than a damaged one. You'd also need to warm the new domain from scratch. Fix the underlying problems instead of running from them.

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