What Is Sender Reputation?

Sender reputation is a score assigned by email service providers (ESPs) like Gmail, Outlook, and Yahoo that determines how your emails are handled — whether they reach the primary inbox, get filtered to spam, or are blocked entirely. Sender reputation operates at both the domain level and IP address level, and is the single most important factor in email deliverability. Sender reputation is built and maintained through several signals: bounce rate (percentage of emails that fail to deliver), spam complaint rate (recipients marking your emails as spam), engagement metrics (open rates, reply rates, link clicks), sending volume consistency, email authentication (SPF, DKIM, DMARC), and blacklist status. A good sender reputation takes weeks to build through proper warmup and can be destroyed in hours by a single campaign with bad data or aggressive sending patterns. For B2B outbound teams, managing sender reputation requires ongoing monitoring and discipline. Key practices include verifying email addresses before sending, maintaining bounce rates below 2%, keeping spam complaint rates below 0.1%, warming up new domains gradually, using separate domains for cold outreach versus transactional email, and monitoring reputation through tools like Google Postmaster Tools. Platforms like Prospect AI manage sender reputation automatically through built-in verification, warmup, and health-aware sending that throttles or pauses accounts showing reputation degradation.