Sender Reputation

Sender reputation is the single most important factor in email deliverability. It's the score that determines whether your messages land in the inbox, the spam folder, or get blocked entirely. Unlike website SEO, sender reputation can degrade rapidly — a single bad week of high bounces and spam complaints can take months to recover from.

The reputation score is domain-specific and IP-specific. Your primary business domain carries a different reputation than your outbound sending domains. Protecting your primary domain is critical: if it gets blacklisted, it affects your transactional email, your team's email, and your brand credibility. This is why experienced cold email operators always use secondary sending domains and never cold email from their primary domain.

Reputation is built through consistent positive signals over time: messages that get opened and replied to, low bounce rates, low spam complaint rates, steady (not spiking) sending volume, and proper authentication. The fastest way to damage reputation is sudden volume spikes, high bounces from unverified lists, or spam complaints from poorly targeted outreach.