The field guide to
making mail land.
12topics — from “what is SPF” to subdomain reputation strategy. Read top to bottom or bookmark the runbooks. The whole guide is platform-neutral; we point out where VoltMail does the work for you in coloured callouts.
// dns records
SPF — Sender Policy Framework
A TXT record that lists which IPs may send mail from your domain. The simplest of the three auth records — and the one most often broken by a forgotten include.
DKIM — DomainKeys Identified Mail
A cryptographic signature on every outbound message. Survives forwarders. Rotates without downtime if you do it right.
DMARC — the policy on top
Tells receivers what to do when SPF and DKIM both fail. The record that makes domain spoofing prohibitive.
BIMI — your logo in the inbox
Authenticates your brand mark next to your sender name in supported clients. Requires DMARC at quarantine or reject, plus a Verified Mark Certificate for Gmail and Apple.
// reputation
Reputation — the meta-signal
Every receiving ISP keeps a score per sending IP and per sending domain. Below threshold, you are in spam. Above, you are in the inbox.
IP warming, the slow build
A new dedicated IP has zero reputation. Send full-volume on day one and you go to spam for weeks. Here is the curve we use.
Feedback loops — when "spam" rings back
AOL, Yahoo, Comcast, and others forward spam complaints back to the sending domain. Listening to them is the fastest way to clean a list.
// compliance
List-Unsubscribe — the new compliance line
Since February 2024 Gmail and Yahoo require a one-click unsubscribe header on every bulk email — and a working endpoint that honours it within 48 hours.
Domain alignment — the invisible check
SPF and DKIM can both pass while DMARC fails. Welcome to the alignment trap, where the From: header and the auth domains have to match.
// operations
Postmaster Tools — the lagged truth
Free dashboards from Google, Microsoft, and others that show your sending health from the receiver's side. 24-72h lagged but invaluable.
Subdomain strategy — isolate your reputations
Marketing should not poison receipts. Mass campaigns should not poison password resets. The cheapest insurance is a sending subdomain per traffic class.
Spam-folder triage — when you wake up to "users say it is in spam"
A 30-minute runbook for the most common cause of "this email never arrived". Works at 9pm on Sunday too.