The first time someone explains email deliverability, it sounds like a setup checklist. Configure SPF. Add a DKIM record. Set a DMARC policy. Send a test. Done.
That is the part that takes an afternoon. The part that takes the rest of the relationship is what happens after.
The seven things that decide whether an email lands
Inbox providers — Gmail, Outlook, Yahoo, Apple, the corporate Microsoft 365 tenants — make a routing decision every time mail from your domain shows up at their gate. The decision is made in milliseconds and it considers, roughly, seven inputs:
- Authentication (SPF, DKIM, DMARC alignment) — does this mail actually come from who it claims to come from
- Sender reputation for the IP and the domain — has this sender behaved well historically
- Engagement signal — are recipients opening, clicking, replying, or marking as spam
- Content shape — is the HTML well-formed, are there suspicious links, is the text-to-image ratio reasonable
- List hygiene — what fraction of sends bounce or hit dead addresses
- Cadence consistency — does this sender send predictably or in spikes
- Recipient action history — has this specific recipient engaged with this sender before
The first one is a setup task. The other six are an ongoing discipline.
Authentication done once, watched forever
SPF, DKIM, and DMARC need to be configured correctly at the start. They also need to be re-verified every time anything changes: a new sending platform, a new transactional service, a new third-party tool that sends from your domain on your behalf. Each addition can break alignment in ways that don't show up in your inbox tests but do show up in Gmail's filters two weeks later.
We re-verify authentication monthly for every client and after any change. The cost of being wrong is six weeks of mystery deliverability decay before anyone connects the dots.
Warm-up isn't a phase — it's a discipline
The standard advice is: when you start sending from a new IP or domain, ramp up slowly. True. The hidden truth is: the warm-up never really ends. Sending volume that drops suddenly and then resumes is treated by inbox providers the same way they treat a new sender — suspiciously. A list that has been silent for six months and then sends to twenty thousand people on Black Friday is not a returning sender. It is a possible spammer.
The cure is the same one we keep recommending: regular, predictable cadence. The Thursday newsletter is not just a marketing rhythm. It is a deliverability practice.
List hygiene without losing growth
Bounces and complaints are deliverability poison. The instinct of most senders is to keep every address that ever subscribed, on the theory that more is better. The math says the opposite: a smaller, engaged list out-delivers a larger, half-engaged list, because every send to a dead inbox lowers the reputation score that decides where the live ones land.
We sunset cold contacts on a rolling schedule — gentle re-engagement first, then quiet removal — so the active list stays clean without anyone feeling kicked off.
What happens when something slips
Even with all of this, things slip. A spam complaint cluster from one campaign. A cold contact list that got imported in a hurry. A new transactional sender misconfigured and sending bounces in your name. We watch the postmaster signals — Google Postmaster Tools, Microsoft SNDS, complaint feedback loops — and notice within forty-eight hours, which is the difference between a small recovery and a long one.
Why this matters
You handed over email so you would not have to think about any of this. You should not. We do, weekly, for every client, in the background. The result is the only result that matters: the email lands in the inbox, the way it did last Thursday, and the Thursday before that.