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What Is Sender Reputation?
TL;DR
Sender reputation is the trust score mailbox providers (Gmail, Outlook, and others) assign to a sending domain and IP based on past behavior — high reputation gets mail delivered to the inbox, low reputation gets it filtered to spam or blocked outright.
What builds or damages sender reputation
Mailbox providers track signals like bounce rate, spam complaints, unsubscribe rate, how often recipients open or reply, and whether authentication records (SPF, DKIM, DMARC) pass. Good numbers on all of these build reputation over time; bad numbers on any of them erode it, often quickly.
Reputation is tracked per sending domain and per IP address (or IP range, if shared). A brand-new domain or IP starts with no reputation at all, which is why warm-up exists.
How reputation affects deliverability
High-reputation senders land in the primary inbox. Middling reputation gets filtered to the promotions tab or spam folder even though it technically "arrived." Reputation that drops far enough can get a domain or IP blocked from sending to a provider entirely, sometimes for weeks.
Reputation is provider-specific: a domain can have strong reputation with Gmail and weak reputation with Outlook at the same time, since each provider runs its own scoring independently.
How to protect sender reputation
The core practices: warm up new domains/IPs gradually, keep bounce rates low by validating email addresses before sending, honor unsubscribes immediately, authenticate every sending domain with SPF/DKIM/DMARC, and monitor for spam complaints. Dedicated IPs also mean your reputation isn’t affected by another sender’s bad behavior on the same IP.
