Reference · the vocabulary, defined properly
Glossary
The vocabulary of email deliverability, defined the way we use it in our tests and reviews. Most terms link to a free tool that checks the thing being defined.
B
D
- Dedicated IP for email/dedicated-ipYour own sending address, your own reputation, nobody else's mess — and a liability below the volume needed to sustain it.
- DKIM/dkimThe cryptographic signature that proves an email wasn't forged or altered — and the ESP default that quietly signs it as someone else.
- DKIM alignment/dkim-alignmentA valid DKIM signature from your ESP's domain proves nothing about yours. Alignment is the d= detail that decides your DMARC fate.
- DMARC/dmarcThe policy layer that tells receivers what to do when SPF and DKIM fail — and the alignment rules that trip up most senders.
- Domain reputation/domain-reputationThe trust score attached to your domain rather than your infrastructure — portable across ESPs, and nearly impossible to outrun.
- Double opt-in/double-opt-inA confirmation click filters out typos, bots and spam traps before they touch your list — if the confirmation email itself gets delivered.
E
- Email feedback loop/feedback-loopWhen a recipient hits 'report spam', a feedback loop tells the sender — if the sender registered, listens, and acts on it.
- Email list hygiene/list-hygieneThe addresses you keep mailing say more about you than the ones you acquire. Hygiene is the discipline of letting the dead ones go.
- Email warm-up/email-warm-upNew domains and IPs start with zero trust. Warm-up is the ramp that builds it — and skipping it is the fastest way to a throttled launch.
G
H
I
- Inbox placement/inbox-placementDelivered and seen are different things. Inbox placement measures where accepted mail actually lands — and it is the metric this site exists to publish.
- IP reputation/ip-reputationThe trust score mailbox providers keep on every sending IP — how it's built, how it's lost, and why delisting doesn't restore it.
M
P
S
- Sender reputation/sender-reputationEvery mailbox provider keeps a running judgment of your sending history. You never see the number — only its consequences.
- Shared IP/shared-ipOn a shared pool your placement rides partly on strangers' behavior — and on how ruthlessly your ESP polices them.
- SMTP/smtpThe transfer protocol behind every email ever sent — and why its politeness is the root of most deliverability problems.
- Soft bounce/soft-bounceA 4xx means temporary — full mailbox, busy server, or a receiver quietly throttling you. The skill is knowing when temporary stops being true.
- Spam complaint rate/complaint-rateEvery 'report spam' click is a recipient testifying against you — and Gmail now publishes exactly how much testimony it will tolerate.
- Spam traps/spam-trapNo human reads a spam trap. Hitting one tells blocklist operators exactly how you built your list — and they act on it.
- SPF alignment/spf-alignmentSPF can pass for a domain your recipients never see. Alignment is DMARC's demand that the passing domain match the visible one.
- SPF records/spf-recordThe DNS record that names which servers may send your mail — and the lookup limit that breaks it the day you add one ESP too many.
- Suppression list/suppression-listUnsubscribes, bounces, complainers — the do-not-send ledger that protects your reputation, until a platform migration leaves it behind.