Deliverability is infrastructure, not luck. A practical checklist for getting back into the primary inbox.
Open rates collapse for two reasons: people stopped caring, or the mailbox provider stopped delivering. Most brands assume the first and never diagnose the second.
Begin with authentication. SPF, DKIM and a DMARC policy are non-negotiable, and misconfiguration here silently routes campaigns to spam regardless of content quality. If you cannot point to a published DMARC record, you are guessing at your deliverability.
Then prune. Subscribers who have not opened in six months actively damage your sender reputation. Segment them into a reactivation flow and suppress the rest. A smaller, engaged list outperforms a large, dormant one on every metric that matters.
Watch your warm-up. Spikes in volume — a sudden campaign to a cold segment, a new IP, a holiday blast — trigger provider suspicion. Ramp gradually and your reputation stays intact.
Content signals count too. Image-to-text ratio, spammy phrasing, a single broken link, and even the subject line length all feed the filtering algorithms. The cheapest way to improve deliverability is to write a better email.
Engagement is the real currency. Opens, clicks, and replies tell the provider that your mail is wanted. Design for the reply, not just the read.
Finally, write something worth opening. Deliverability buys you the chance to be read; it does not buy attention. The best technical setup in the world cannot rescue a boring subject line.
Segment before you send, not after you panic. A single broadcast to a list of mixed intent punishes your most engaged readers with content that is irrelevant to them, and they are the ones whose attention you can least afford to lose. Behavioural cohorts keep the relevance bar high.
Measure the journey, not just the open. Click-through, reply rate, and downstream conversion tell you whether the email did its job; an open only tells you the subject line worked. Optimise toward the action that pays, and the vanity metrics will follow on their own.
