Deliverability is the invisible layer under every email metric. Before a subject line can win an open, mailbox providers decide whether the message reaches the inbox at all, and they make that call based on your authentication, your sending patterns, and how recipients have treated your mail in the past.
Authentication is table stakes
Three DNS records prove you are who you claim to be. SPF lists which servers may send for your domain. DKIM cryptographically signs each message. DMARC tells receivers what to do when a message fails the first two checks, and major providers now require it for bulk senders alongside one-click unsubscribe and low spam-complaint rates. If these are not in place, nothing else on this page matters.
Your list is your reputation
- Never purchase lists; the addresses are stale and seeded with spam traps.
- Use confirmed opt-in where signup quality is questionable.
- Remove hard bounces immediately and automatically.
- Sunset chronic non-openers; mailing people who never engage tells providers your mail is unwanted.
Engagement is the ranking signal
Mailbox providers watch what recipients do: opens, replies, and moves to folders count for you; deletions without reading and spam complaints count heavily against you. This is the hidden case for segmentation, because concentrating sends on engaged recipients lifts the reputation of every message you send.
Watch the dashboards
Register for Google Postmaster Tools and monitor your spam complaint rate, keeping it well under 0.3 percent. Track bounce rates per campaign, and warm up any new domain or IP gradually before sending at full volume. Deliverability problems build slowly and silently, and the senders who notice early are the ones watching.