FIELD GUIDE
Email deliverability basics: authentication and list hygiene
Deliverability starts with two fundamentals: authenticate your domain and keep your list clean. Authentication, SPF, DKIM and DMARC, tells inbox providers your mail is really yours. Hygiene, removing bounces and dead addresses and honouring unsubscribes, keeps complaint rates low so reputation holds. This guide covers those basics. Diagnosing and warming a new sending domain is a separate scope and not covered here.
The three authentication records
Three DNS records authenticate your mail. SPF lists which servers may send for your domain, so a receiver can reject mail from anywhere else claiming to be you. DKIM signs each message with a key that proves it was not altered and that it came from your domain. DMARC ties the two together: it tells receivers what to do when a message fails SPF or DKIM, and it sends you reports so you can see who is mailing as you. Set all three, publish DMARC in monitoring mode first, then tighten the policy once your legitimate mail passes. Without them, even honest mail lands in spam or is refused.
List hygiene
A clean list is a deliverability tool, not just tidiness. Remove hard bounces immediately, because repeatedly mailing dead addresses signals a careless sender. Suppress addresses that have not engaged in a long time rather than mailing them forever; low engagement drags your reputation down for everyone on the list. Honour unsubscribes instantly and make them easy, since a frustrated recipient hitting spam is far more damaging than a lost subscriber. Watch your complaint rate as the number that matters most. When you migrate platforms, carry your bounces and unsubscribes across as suppressions so a fresh account does not repeat old mistakes. The list cleaning guide covers this in detail.
Engagement and reputation
Inbox placement is earned by engagement, not just configuration. Providers watch whether people open, reply, and keep your mail out of spam, and they weight recent behaviour heavily. Mail the people who want it, and mail them consistently rather than in rare giant blasts, because both silence and sudden spikes look abnormal. Segment out the chronically unengaged before they cost you placement with everyone else. Keep sending volume steady and content recognisable. None of this compensates for missing authentication or a dirty list, but with those in place, consistent engagement is what moves you from the promotions pile toward the primary inbox and keeps you there.
What this guide does not cover
One thing this guide deliberately does not cover: diagnosing and warming up a brand-new sending domain or IP. That is a distinct discipline, ramping volume gradually, monitoring per-provider reputation as it builds, and troubleshooting a cold domain, and it belongs to dedicated warmup tooling rather than these fundamentals. The basics here, authentication and hygiene, apply whether your domain is established or new, but if you are standing up fresh sending infrastructure, treat warmup as its own separate project with its own diagnostics. Do not assume good SPF, DKIM and DMARC alone will carry a cold domain; they are necessary, not sufficient, for that specific case.
Questions people also ask
Which record matters most, SPF, DKIM or DMARC?
None on its own. DMARC only works when SPF and DKIM are in place, because it decides what to do based on their results. Set all three, publish DMARC in monitoring mode first, then tighten the policy once your legitimate mail passes cleanly.
Does authentication guarantee the inbox?
No. Authentication is necessary but not sufficient. It proves your mail is genuinely yours, but placement is then decided by list hygiene and by how recipients engage. A well-authenticated dirty list still lands in spam.