Authentication (SPF, DKIM, DMARC) is now mandatory, not optional — without it, bulk mail to Gmail and Yahoo gets blocked or junked.
Engagement is the real deliverability signal: mailbox providers watch opens, clicks, and complaints to decide where you land.
Sunset unengaged subscribers aggressively — a smaller, active list out-delivers a large, stale one.
Keep complaint and bounce rates low and send volume steady; spikes and spam reports are what tank a sender reputation.
Authentication is the price of entry now
Since the major mailbox providers tightened their bulk-sender rules, proper authentication stopped being a nice-to-have and became a requirement. SPF tells receivers which servers may send for your domain, DKIM cryptographically signs your mail so it cannot be forged, and DMARC ties the two together with a policy telling receivers what to do with mail that fails. Without all three configured correctly, large sends to Gmail and Yahoo are increasingly blocked or routed straight to spam.
Get these records right once and they protect every campaign afterwards. A DMARC policy at quarantine or reject, in particular, signals that you take your domain's reputation seriously — which is exactly the signal mailbox providers reward with inbox placement.
Engagement decides where you land
Authentication gets you in the door; engagement decides which room you end up in. Mailbox providers watch how recipients treat your mail — do they open it, click it, reply, or mark it as spam — and use those signals to place future sends in the inbox or the junk folder. A list that opens and clicks tells Gmail your mail is wanted; a list that ignores or reports it does the opposite.
This is why list quality beats list size. Sending to people who never engage drags down your reputation for everyone, including the subscribers who do want to hear from you. The goal is a list where a healthy share of recipients actively engage, because that is the behaviour that keeps you in the inbox.
Sunset the deadweight
The single most effective deliverability habit is aggressively retiring unengaged subscribers. Contacts who have not opened anything in six months are not just neutral — they actively harm you, because sending to them lowers your engagement rates and raises your spam-complaint risk. A disciplined sunset policy that suppresses or removes long-dormant addresses keeps your engagement metrics strong and your sender reputation healthy.
It feels counterintuitive to shrink your list on purpose, but a smaller, engaged list reliably out-delivers a large, stale one. You are trading vanity list size for the thing that actually matters: landing in the inbox.
Keep the operational signals clean
Beyond authentication and engagement, a handful of operational metrics govern deliverability. Keep spam-complaint rates well under the provider thresholds, hold bounce rates low by cleaning invalid addresses, and maintain a one-click unsubscribe so frustrated recipients leave quietly instead of hitting the spam button. Just as important, keep your send volume steady — sudden ten-fold spikes look like compromised-account behaviour and trip spam filters.
Treat deliverability as ongoing hygiene, not a one-time setup. Monitor these signals, warm up new sending domains gradually, and fix problems early. The senders who consistently reach the inbox are the ones who respect these mechanics every send, not just when something breaks.
Common mistakes that quietly kill results
These come straight from audits we run every week. If any of them stings, you’re in good company — and the fix is usually faster than you think.
One welcome email instead of a flow. Subscribers are hottest in the first 72 hours. A 4-6 email welcome series spread over two weeks routinely drives 3-5× the revenue of a single 10%-off blast.
Blasting the whole list every time. Untargeted sends train inboxes to ignore you and tank deliverability. Even two segments — engaged 90 days vs. everyone else — typically lifts open rates 30-50% on the engaged side.
SMS as email's louder twin. SMS earns 10-20× email's attention; spend it on time-sensitive moments only — drops, restocks, delivery. Two campaigns a month, max, or your unsubscribe rate writes the ending.
Flows set up once and never audited. Your abandoned-cart flow from 2024 references products you discontinued. Quarterly flow audits — links, offers, timing, branching — take an hour and routinely recover 10-20% lost revenue.
From the trenches
One client's abandoned-cart flow converted at 4.1%. We added a second email with three customer reviews and a photo, nothing else. 6.8%. The discount they were planning would have cost more and converted less.
Quick checklist before you ship
Abandoned cart: 3 touches at 1h / 24h / 72h, second one includes social proof
Mobile preview checked on an actual phone before send
Revenue per recipient tracked, not just open rate
Sunset policy live: unengaged 150+ days suppressed automatically
Segments: at minimum engaged-90, lapsed, VIP by spend
Welcome flow: 4+ emails, first one inside 5 minutes of signup
Every campaign has one job and one primary CTA
Frequently asked questions
What are the most important email deliverability settings?
Correct SPF, DKIM, and DMARC authentication are now mandatory for bulk senders. Beyond that, one-click unsubscribe headers and low complaint and bounce rates are essential for inbox placement.
Why is my email going to spam?
Usually a mix of weak authentication and poor engagement. If recipients ignore or report your mail, providers route future sends to spam. Fix your SPF/DKIM/DMARC, then improve list quality and engagement.
Should I remove inactive email subscribers?
Yes. Subscribers who have not engaged in six months or more drag down your engagement metrics and raise complaint risk. A smaller, active list reliably out-delivers a large, stale one.
Senior Growth Strategist at GrowwithBA. 12 years running SEO, paid media, and retention for ecommerce and SaaS brands from $1M to $100M+. Every guide here comes from live client work — not theory.
Marketing operators, founders, and in-house teams looking for tactical guidance, not generic high-level advice. Particularly useful if you have hands-on responsibility for execution.
What's the source of these recommendations?
Real client engagements at GrowwithBA, a a hands-on team marketing agency with offices in Nagpur, India and Dover, Delaware, USA. Founded in 2014.
When was this last updated?
2026. The web is full of outdated marketing advice; we update guides as platforms and best practices change.
Is this AI-generated content?
No. Written by senior marketing operators based on actual client work. Reviewed and updated regularly. Real outcomes, real tradeoffs, real costs, not generic templated content.
How can I get help implementing this?
Book a free 30-minute audit with our team. We'll review your current setup and give you a prioritized action list, no sales pitch, no obligation.