Blog (page 3)
Insights on email authentication, deliverability and security.
218 articles, page 3 of 5
SendGrid dedicated IPs, authentication and reputation
Most teams reach for a SendGrid dedicated IP because someone told them shared IPs are bad, or because a deliverability vendor implied that owning your own IP is the professional thing to do.
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p=none vs quarantine vs reject
The three DMARC policies compared: what p=none, p=quarantine and p=reject each tell receivers to do with failing mail, and how to progress between them safely without breaking your own email.
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Bounce handling and the return-path
The envelope return-path is where bounces come back to and the domain SPF authenticates. Here is how a custom return-path on your own subdomain fixes SPF alignment under DMARC, and what really happens to a bounce.
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DMARC for Mailchimp users: a deliverability checklist
If you send marketing email through Mailchimp, you sit in an awkward spot. You do not run your own mail servers, you do not control the IP addresses your campaigns go out on, and yet your From: address still says.
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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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CMC: BIMI for unregistered logos
A Common Mark Certificate lets brands without a registered trademark show a verified BIMI logo. Here is how a CMC is checked, how it differs from a VMC, and where it is accepted today.
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DNSSEC and email security: what it does and does not do
DNSSEC turns up in almost every conversation about hardening email, usually as a vague recommendation: "you should enable DNSSEC". The advice is rarely wrong, but it is almost never explained.
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How invoice fraud begins with a spoofed domain
Invoice fraud usually starts with a forged sender address. Here is how exact-domain spoofing works, what DMARC at p=reject stops, and what it does not.
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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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Dangling DNS records as an email risk
Stale CNAMEs, SPF includes and DKIM selectors that point to resources you no longer own quietly delegate your sending authority to whoever claims them next. Here is how dangling DNS becomes a real spoofing and SPF risk, and how to find and close the gaps.
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Automating DMARC, SPF and DKIM with the DMARC Engine API
Most teams start with email authentication as a one-off project: someone fixes the SPF record, publishes a DKIM key, sets a DMARC policy, and moves on.
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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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Dedicated vs shared sending IPs
Dedicated and shared sending IPs carry very different reputation trade-offs, and the right choice hinges on sustained volume, not folklore. Here is who should use which, and how the decision changes SPF, DKIM and DMARC alignment, plus what your aggregate reports reveal.
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How to reach DMARC p=reject without breaking email
The staged playbook to DMARC enforcement with no email outage: inventory senders, fix SPF and DKIM, ramp p=none to p=reject, and lock down subdomains.
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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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Designing a logo that passes BIMI
A BIMI logo is not your website logo exported to SVG. It is a purpose-built coin: square canvas, solid background, the mark centred in a circular safe zone, and the SVG Tiny PS shell added by hand. Here is how to design one that reads clearly at avatar size and gets past the validators.
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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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DKIM canonicalisation: simple vs relaxed
The DKIM c= tag decides whether your signature survives the journey to the inbox. Here is exactly what simple and relaxed canonicalisation do to headers and body, why relaxed tolerates the reformatting that real mail servers perform, and where simple still causes intermittent body-hash failures.
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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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DMARC external destination verification
Sending DMARC reports to an address outside your own domain is an external destination, and RFC 7489 requires the receiving domain to authorise it first. Here is exactly which DNS record to publish, where, and why reports silently vanish without it.
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How to enable DKIM in Google Workspace
A step-by-step guide to enabling DKIM for a Google Workspace domain: generating a 2048-bit key in the Admin console, publishing the public key as a DNS TXT record (including the 255-byte chunking that trips people up), verifying it is live, and turning on signing safely in the right order.
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Why DMARC fails when SPF and DKIM pass
SPF passes, DKIM passes, yet DMARC still fails on legitimate mail. The cause is almost always alignment: both checks authenticated a domain other than the one in your From header. Here is how to find the misaligned identifier in a single message header and across all sources in your aggregate reports, then fix each cause.
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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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DMARC says quarantine but mail still reaches the inbox
A quarantine policy does not always mean the spam folder. Here is why failing mail still lands in the inbox: pct sampling, alignment, receiver discretion, DNS caching, and exactly what to check.
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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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DMARC reporting: mailto vs https URIs
The rua and ruf tags accept both mailto: and https: URIs, but almost every working DMARC record uses mailto: only. Here is why HTTPS delivery is dead in practice, how the size-limit suffix and external destination verification work, and how analysers ingest the gzipped XML.
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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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DMARC reports show sources I do not recognise
Unknown sending IPs in your DMARC aggregate reports are normal, not an emergency. Here is a reliable four-question triage to tell shadow IT and forwarders from real spoofers, and exactly what to do with each.
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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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DMARC vs SPF vs DKIM: how they fit together
SPF, DKIM and DMARC are named together so often that they blur into one thing. They are not. This is a clear comparison of what each record actually proves, why SPF and DKIM are blind to the From line your recipients trust, and how DMARC ties them together with alignment and policy.
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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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Double opt-in and why it matters
Confirmed (double) opt-in keeps spam-trap hits, bounces and complaints off your list, the exact reputation signals that decide whether your authenticated mail reaches the inbox and clears the Gmail and Yahoo bulk-sender rules.
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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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Email authentication for accountants
Accountancy practices are prime impersonation targets: you hold client bank details, your clients act on what you tell them, and the tax calendar is public. This guide covers the four fraud patterns a practice actually faces, exactly where DMARC, SPF and DKIM stop them, and a deadline-aware enforcement plan to reach p=reject without breaking client 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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Email authentication for ActiveCampaign: SPF, DKIM and DMARC
An ActiveCampaign-specific guide to email authentication: the exact SPF include, CNAME-based DKIM, the custom return-path that aligns SPF, and a staged path to DMARC p=reject without breaking your campaigns or automations.
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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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Email authentication for Amazon SES: SPF, DKIM and DMARC
Amazon SES passes SPF and DKIM by default but on amazonses.com, so nothing aligns under DMARC. Here is the exact SES include, Easy DKIM and its CNAME selectors, the custom MAIL FROM that fixes SPF alignment, and the staged path to p=reject.
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Why Gmail, Yahoo and Microsoft now require DMARC
Gmail, Yahoo and Microsoft now require SPF, DKIM and DMARC from bulk senders. Here is what each demands, what "require" really means, and how to comply.
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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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Email authentication for Amazon WorkMail: SPF, DKIM and DMARC
Amazon WorkMail sends through SES, so its defaults quietly fail DMARC alignment. Here is the exact SPF include, the three Easy DKIM CNAMEs, the custom MAIL FROM domain that fixes SPF alignment, and the staged path to p=reject without an outage.
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The 2024 and 2025 bulk-sender requirements in full
Google, Yahoo and Microsoft turned email authentication into a hard delivery gate. Here are the exact requirements, the numeric thresholds, who counts as a bulk sender, and a line-by-line compliance checklist.
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Email authentication for Brevo: SPF, DKIM and DMARC
A Brevo-specific guide to SPF, DKIM and DMARC: the exact spf.brevo.com include, both DKIM CNAME selectors, why the return-path means DKIM (not SPF) carries DMARC on shared IPs, custom return-path with a dedicated IP, and the staged path from p=none to p=reject without breaking delivery.
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Keeping your spam complaint rate under 0.3%
The spam complaint rate is the small, unforgiving number mailbox providers trust most. Learn how it is measured per provider, what pushes it past the 0.3% danger line, and the concrete steps that bring it back down.
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Email authentication for Constant Contact: SPF, DKIM and DMARC
Constant Contact sends your campaigns from its own servers under your brand's From address, so by default SPF and DKIM both align to Constant Contact, not you, and DMARC fails. This Constant Contact-specific guide covers self-authentication, the real ccsend.com DKIM CNAMEs, when SPF and a branded return-path matter, and the safe staged path from p=none to p=reject without losing a campaign.
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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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Email authentication for e-commerce
Online shops send order, shipping and receipt mail from a dozen different systems at once. Here is how to authenticate every stream, meet the Gmail, Yahoo and Microsoft bulk-sender rules, block order-confirmation phishing, and earn your brand logo in the inbox with BIMI.
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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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