Reference
DMARC, SPF, DKIM & BIMI glossary
Plain-English definitions of the DMARC, SPF, DKIM, BIMI and deliverability terms you will meet, each with a tool to check it.
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Aggregate report (RUA)DMARC aggregate (RUA) reports are daily XML summaries from receivers showing how your mail authenticated and aligned.ARC (Authenticated Received Chain)An email standard that preserves authentication results across intermediaries so legitimate forwarded mail is not wrongly rejected.
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DANEDANE uses DNSSEC-signed DNS records to tell sending servers which TLS certificate a mail server should present.Display-name spoofingA scam where the sender's friendly display name is forged to look trusted, even though the real email address is unrelated.DKIMA cryptographic signature added to outgoing email that lets receivers verify the message was not altered and came from your domain.DKIM key rotationPeriodically replacing a DKIM signing key with a fresh keypair and publishing the new public key under a new selector.DKIM selectorA label in a DKIM signature that points receivers to the right public key in your DNS.DMARCA DNS policy that tells receivers what to do with email that fails SPF and DKIM authentication checks for your domain.DMARC alignmentAlignment means the domain authenticated by SPF or DKIM matches the visible From domain, which is what DMARC actually checks.DMARC policy (p=none/quarantine/reject)The p= tag in a DMARC record tells receivers what to do with mail that fails DMARC: monitor, quarantine or reject.DNSBL (blocklist)A DNS-based blocklist of IP addresses or domains known for sending spam, used by mail servers to filter inbound mail.DNSSECDNSSEC cryptographically signs DNS records so resolvers can detect tampered or forged answers.
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Email deliverabilityHow reliably your legitimate email reaches the inbox rather than the spam folder or being rejected.Email spoofingForging a message's sender so it appears to come from a domain or person it does not, used in phishing and fraud.ESP (Email Service Provider)A third-party platform that sends email on your behalf, such as marketing, transactional or newsletter services.
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FCrDNS (forward-confirmed reverse DNS)A check confirming that a sending IP's reverse DNS name resolves back to the same IP, signalling a properly configured mail server.Forensic report (RUF)DMARC forensic (RUF) reports are per-message failure samples sent in near real time when a message fails DMARC.
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pct tagThe DMARC pct tag tells receivers what percentage of failing mail to apply your policy to, so you can roll out enforcement gradually.PermErrorA permanent SPF error, meaning the published record is broken or unprocessable and cannot give a pass.PhishingFraudulent messages that impersonate a trusted sender to trick recipients into revealing data or making payments.PTR recordA reverse-DNS record that maps an IP address back to a hostname, used by mail servers to vet who is connecting.
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SMTPThe standard protocol mail servers use to transfer email from sender to recipient across the internet.SPFA DNS TXT record listing which servers may send email for your domain, checked against the message's return-path.SPF 10-lookup limitSPF allows at most 10 DNS lookups when evaluating a record; exceeding it causes a permerror and the SPF check is effectively void.SPF flatteningSPF flattening replaces include and other lookups in an SPF record with the resolved IP addresses to stay under the 10-lookup limit.SPF qualifiers (-all, ~all)The qualifier on the final all mechanism that tells receivers how to treat mail from unlisted senders.STARTTLSAn SMTP command that upgrades a plain-text email connection to an encrypted TLS session on the same port.Subdomain policy (sp)The DMARC sp tag sets a separate policy for subdomains, overriding the main p tag for any subdomain without its own DMARC record.SVG Tiny PSThe restricted SVG image profile required for BIMI brand logos displayed next to email in the inbox.