Tagged “dmarc” (page 3)
153 articles, page 3 of 4
Email authentication for Postmark: SPF, DKIM and DMARC
A Postmark-specific guide to SPF, DKIM and DMARC: the exact spf.mtasv.net include, publishing the DKIM CNAME selectors, configuring a custom Return-Path for SPF alignment, and ramping safely from p=none to p=reject without breaking transactional mail.
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Email authentication for Proofpoint: SPF, DKIM and DMARC
Proofpoint is a gateway, not an ESP, so it relays your mail from its own IPs and that quietly breaks SPF and DKIM alignment. This Proofpoint-specific guide gives the exact SPF mechanism for Essentials (a:dispatch-us.ppe-hosted.com) and the cluster include for Protection Server, the DKIM signing and selector workflow for both products, how the return path affects SPF alignment, and the staged path to p=reject with Proofpoint in front of Microsoft 365 or Google Workspace.
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Email authentication for Proton Mail: SPF, DKIM and DMARC
A Proton Mail-specific guide to SPF, DKIM and DMARC on a custom domain: the exact _spf.protonmail.ch include, Proton's three rotating DKIM CNAME records, the return-path quirk that makes DKIM load-bearing for alignment, and a safe path to p=reject.
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Email authentication for Salesforce: SPF, DKIM and DMARC
Salesforce is four senders, not one. Here are the exact SPF includes, how to generate and activate Salesforce DKIM CNAMEs, why bounce management breaks SPF alignment, and the staged path to p=reject across core, Marketing Cloud and Pardot.
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Email authentication for SendGrid: SPF, DKIM and DMARC
A SendGrid-specific guide to SPF, DKIM and DMARC: the exact sendgrid.net include, Domain Authentication with the s1/s2 DKIM selectors, the custom return-path for SPF alignment, and the staged path to p=reject without breaking your mail.
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Email authentication for SparkPost: SPF, DKIM and DMARC
A SparkPost-specific guide to SPF, DKIM and DMARC: the exact _spf.sparkpostmail.com include, the scph DKIM TXT record, the bounce-domain CNAME that makes SPF align, and how to reach p=reject without losing SparkPost mail.
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Email authentication for Zendesk: SPF, DKIM and DMARC
Zendesk locks the Return-Path to its own domain, so SPF can never align and DKIM is the only mechanism that carries your DMARC pass. Here are the exact zendesk1 and zendesk2 CNAMEs, the mail.zendesk.com SPF include, the safe order of operations and how to reach p=reject without breaking support email.
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Email authentication for Zoho Mail: SPF, DKIM and DMARC
A Zoho Mail-specific guide to SPF, DKIM and DMARC: the exact Zoho SPF include, how to generate and publish DKIM selectors in the Admin Console, the return-path and alignment quirks that decide whether DMARC passes, and a safe sequence from p=none to p=reject.
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Fix: BIMI logo not showing in Gmail
Gmail shows a grey initial instead of your BIMI logo and never says why. Here is every reason it fails, in the order Gmail checks them: DMARC not at enforcement, a missing VMC, an SVG that breaks the Tiny PS profile, a logo-to-certificate mismatch, and cached negative results, plus how to fix each.
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Fix: DKIM fails after forwarding
Forwarders and mailing lists break DKIM by changing the message body and headers, not the connection. Here is exactly what fails, what survives, where ARC helps, how to spot forwarding failures in your DMARC reports, and how to reduce the impact without parking at p=none.
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Fix: DKIM public key not found in DNS
The "DKIM public key not found in DNS" error is almost always a naming or publishing problem, not a broken key. Here is exactly which name receivers query, why it returns nothing, how CNAME and TXT publishing differ, and how to confirm the key resolves end to end.
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Fix: DKIM signature did not verify
"DKIM signature did not verify" is at least six different problems wearing one error string: body hash mismatch, no key in DNS, malformed record, key mismatch after rotation, expired signature, or a key too short. Here is how to read the exact reason in the brackets and apply the one correct fix for each.
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Fix: MTA-STS policy not found
"MTA-STS policy not found" is never one problem: it is a five-link chain (DNS TXT, HTTPS host, certificate, file path, file content) plus the MX-coverage trap, and it fails silently because senders fall back to opportunistic TLS rather than bounce. Walk the discovery the way a sending MTA does, with real dig, curl and openssl checks, and fix the first broken link.
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Fix: multiple SPF records
Two SPF records on one domain force a permanent PermError that silently strips a DMARC route. Here is why it happens, how receivers treat it, and how to merge two records into one compliant record without losing a sender or blowing the 10-lookup limit.
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Fix: SPF TempError
An SPF TempError is a transient DNS failure, not a broken record. Here is what it means, why it differs from PermError, how Google, Yahoo and Microsoft treat it under SPF and DMARC, and the concrete steps that make your SPF resolution reliable.
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Fix: SPF too many DNS lookups
SPF caps you at ten DNS-querying mechanisms, counted after every include expands into its provider's nested netblocks, which is why a record with five includes can spend fifteen lookups and PermError. Here is how to count the budget, prune the includes that overspend it, and flatten or consolidate back under the limit before enforcement makes the failure bite.
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Free checkers vs paid DMARC platforms
Free DMARC checkers read the current state of your DNS in one lookup, and they do that job completely. Enforcement is different: getting a domain from p=none to p=reject without dropping legitimate mail is a multi-week process driven by the continuous aggregate-report stream, which no one-shot tool can ever surface. This guide draws the exact line between what free checkers do well, where they structurally stop, and what a managed platform adds, plus an honest account of who needs the paid side and who does not.
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Header-From vs envelope-from: the two From addresses
Every email carries two different From addresses: the header-from (RFC5322.From) that humans see and the envelope-from (RFC5321.MailFrom) used for bounces. SPF checks one, DMARC checks the other, and the gap between them explains alignment, forwarding breakage and spoofing.
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Hosted vs do-it-yourself DMARC
DIY DMARC looks free, but the real cost lives in senior time, the risk of breaking your own mail on the way to enforcement, and the monitoring tail nobody keeps up. Here is how to price hosted versus do-it-yourself honestly, and decide which your domain actually needs.
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Relaxed vs strict DMARC alignment
DMARC does not check whether SPF or DKIM passed, it checks alignment. The aspf and adkim tags decide how exact that match must be. Here is when strict alignment is worth it, when relaxed is right, and exactly how the choice reshapes subdomain sending.
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RFC 7489: the DMARC standard explained
A close reading of RFC 7489, the document that defines DMARC: the From-header trust model, identifier alignment, the record tags, policy discovery and application, the two report types, and the clauses people consistently misread.
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ARC: Authenticated Received Chain explained
Forwarding and mailing lists break SPF and DKIM in transit, flipping a passing message to a DMARC failure. ARC, the Authenticated Received Chain, preserves the original authentication verdict across intermediaries with a signed, tamper-evident chain, so trusted forwarders can vouch for legitimate mail and you can reach p=reject without breaking list traffic.
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How BIMI displays in Gmail and Apple Mail
Gmail and Apple Mail both reward an enforced DMARC domain with a verified logo, but each shows it differently and both demand a certificate. Here is what each provider displays, why a Verified Mark Certificate is non-negotiable, and how to test the whole BIMI chain before you rely on it.
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Display-name spoofing and why DMARC misses it
Friendly-from spoofing impersonates a person using a domain the attacker legitimately controls, so it passes DMARC every time by design. Here is why DMARC cannot catch it, where it shows up in BEC and CEO fraud, and the layered controls that actually mitigate it.
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How to rotate DKIM keys safely
DKIM signing keys decay in security the longer they live. This guide shows how to rotate them using selectors, with full overlap and verification, so legitimate mail never drops a signature or fails DMARC during the change.
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DMARC alignment explained, with examples
A message can pass SPF and verify DKIM yet still fail DMARC. The reason is alignment. This guide explains SPF and DKIM alignment, relaxed versus strict mode, and the exact DMARC pass rule, with five worked examples of messages that pass and fail.
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Ten common DMARC mistakes and how to avoid them
The configuration and rollout mistakes that most often break mail or leave domains exposed, from jumping straight to p=reject to ignoring report drift, and exactly how to avoid each one.
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Protecting parked and no-mail domains
Domains that never send mail are the easiest to secure and the most commonly left wide open. Here is how to lock down parked, legacy and campaign domains with SPF -all, DMARC p=reject and a null MX so they cannot be spoofed, with zero deliverability risk.
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DMARC for Google Workspace
A new Google Workspace domain ships with no DKIM signing, an SPF record you must add yourself, and no DMARC policy at all. This guide walks the exact order to fix that: get SPF right under the 10-lookup limit, switch on DKIM in the Admin console, then ratchet DMARC from monitoring to full reject without breaking a single legitimate message.
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DMARC for Microsoft 365
A practical, ordered guide to email authentication on Microsoft 365: build a complete SPF record for Exchange Online, enable DKIM signing with Microsoft's two selector CNAMEs, and walk DMARC safely from p=none through quarantine to p=reject without breaking your mail.
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The DMARC pct tag and sampling, explained
The pct tag was DMARC's sampling dial until RFC 9989 removed it. How legacy receivers still apply it, why pct=0 was a downgrade trap, and how to migrate off it safely.
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The DMARC record explained, tag by tag
A plain-English reference to every tag in a DMARC record: v, p, sp, rua, ruf, pct, adkim, aspf, fo, rf and ri. What each one does, the exact syntax it expects and the sensible default to reach for.
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What DMARC reports do and do not tell you
Passing DMARC is permission to be judged on your merits, not a guaranteed seat in the inbox. Here is how to read aggregate reports for exactly what they measure, identity and authentication, without mistaking a perfect pass rate for good deliverability or panicking at failures that do not matter.
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DMARC aggregate vs forensic reports
DMARC sends two kinds of feedback: aggregate (rua) reports and forensic (ruf) reports. They answer different questions and carry very different privacy risks. This guide explains exactly what each contains, why forensic reports have all but vanished, the data-protection considerations on both sides, and how to turn the aggregate data into a safe path from p=none to p=reject.
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Subdomain policy: the DMARC sp tag
An enforced root domain at p=reject protects exactly one address and can leave every subdomain spoofable. Here is what the DMARC sp tag does, the inheritance trap that catches teams mid-migration, and how to close the gap safely without bouncing legitimate subdomain mail.
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How email spoofing actually works
Email spoofing takes no password and no exploit: SMTP simply trusts whatever the sender types into the From field. This guide traces the mechanism from the raw SMTP conversation, through the crucial split between the envelope-from used for delivery and the header-from a human reads, to the three layered controls (SPF, DKIM and DMARC alignment) that finally make forging your domain fail.
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Email transport security: STARTTLS, MTA-STS, DANE
DMARC proves who sent a message, but it does nothing to protect that message while it crosses the internet. Here is how opportunistic STARTTLS, MTA-STS, DANE and TLS-RPT work together to keep inbound mail encrypted in transit, why STARTTLS alone is trivially downgraded, and the safe order to deploy enforcement without bouncing legitimate mail.
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How to enable DKIM in Microsoft 365
Microsoft 365 signs your mail with a shared Microsoft domain by default, which does nothing for DMARC alignment. This guide walks through enabling DKIM signing for your own custom domain end to end: finding the exact CNAME values, publishing the two selector records, switching signing on, and verifying the result really passes.
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How to fix SPF PermError
SPF PermError means a receiver tried to evaluate your SPF record and gave up, so SPF stops counting towards DMARC. This guide diagnoses PermError, TempError and the ten-lookup limit, then walks through a step by step repair process.
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Why forwarding breaks email authentication
Forwarding almost always breaks SPF and sometimes breaks DKIM too. Here is what survives a forwarding hop, why DKIM is the mechanism that carries your authentication through, how DMARC's one-aligned-pass rule copes, and where ARC rescues mailing-list mail.
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Lookalike and cousin domains
Attackers register confusable domains that authenticate perfectly and slip past your defences, because your DMARC policy protects only the exact name it is published under. Here is how homoglyph and cousin domains work, the precise reason a p=reject policy cannot touch them, and the layered plan that actually defends your brand.
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One-click unsubscribe: the List-Unsubscribe requirement
Google, Yahoo and Microsoft now require working one-click unsubscribe on bulk mail. Here is what the List-Unsubscribe and List-Unsubscribe-Post headers are, how RFC 8058 one-click actually works on the wire, how to implement it correctly, and why it sits alongside SPF, DKIM and DMARC on the same deliverability checklist.
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PCI DSS 4.0, cyber-insurance and email authentication
PCI DSS 4.0 Requirement 5.4.1 and cyber-insurance questionnaires now treat anti-phishing as a measurable control. Here is exactly how that intersects with DMARC, SPF and DKIM, what counts as evidence, and how to reach enforcement without breaking your own mail.
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Phishing and business email compromise
Business email compromise rarely uses malware: it borrows trust by impersonating people you already deal with. Here is how phishing and BEC work, where the money goes, and the layered defences, with DMARC at enforcement as the load-bearing wall.
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Publishing DMARC, SPF and DKIM on common DNS hosts
Exact steps to publish SPF, DMARC and DKIM on Cloudflare, GoDaddy, Namecheap and AWS Route 53, plus the two gotchas that break most setups: TXT chunking on long DKIM keys and CNAME coexistence at the apex.
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How sender reputation works
Mailbox providers decide where your mail lands based on sender reputation, a private estimate built from how recipients react to your messages and how cleanly you send. This guide explains domain and IP reputation, the signals that raise and lower them, how to warm up a new sender, and why aligned SPF, DKIM and DMARC are what keep the reputation you build genuinely yours.
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The SPF 10-lookup limit, explained
SPF caps how much DNS work a receiver may do when evaluating your record. Go over the 10-lookup limit, or the separate void-lookup limit, and SPF returns a permerror that quietly stops helping your DMARC result. Here is how includes consume the budget, why exceeding it breaks SPF, and how to get safely back under the line.
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SPF ~all vs -all vs ?all
Soft fail, hard fail, neutral and pass-all: what each SPF qualifier on the all mechanism actually instructs receivers to do, how DMARC changes the picture, and which one to publish at each stage of your rollout.
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