Blog (page 3)
Insights on email authentication, deliverability and security.
190 articles, page 3 of 4
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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Email authentication for schools and universities
A practical, stage-by-stage path to DMARC enforcement on a sprawling .edu or .ac.uk estate: discovery, fixing SPF under the ten-lookup limit, aligning DKIM across many departmental senders, ramping to p=reject, and the governance traps that stall most rollouts.
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SPF flattening: what it is and when you need it
SPF flattening replaces lookup-based mechanisms with raw IP ranges to dodge the ten-lookup limit. It works, but a hand-flattened record silently goes stale. Here is what flattening really does, the trade-offs, why doing it by hand is risky, and how hosted flattening stays current automatically.
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Email authentication for Fastmail: SPF, DKIM and DMARC
A Fastmail-specific setup guide: the exact spf.messagingengine.com SPF include, the three fm1/fm2/fm3 DKIM CNAMEs, how return-path and DKIM alignment behave, and the safe path from p=none to p=reject.
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SPF records for common email providers
The correct, current SPF includes for Google Workspace, Microsoft 365, Mailchimp, SendGrid, Amazon SES and more, plus how to combine several providers in one record without breaking the 10-lookup limit.
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Email authentication for financial services
For banks, insurers and fintechs, DMARC, SPF, DKIM, MTA-STS and BIMI are anti-fraud and brand-protection controls, not deliverability tweaks. How to meet regulatory expectations and reach p=reject across a multi-vendor estate without breaking OTP or statement mail.
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What is BIMI and is it worth it?
BIMI puts your brand logo beside authenticated mail, but only after DMARC enforcement and, for the big providers, a paid certificate. Here is what it shows, what it costs, and an honest view of who actually benefits.
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Email authentication for Freshdesk: SPF, DKIM and DMARC
A Freshdesk-specific setup guide: the exact SPF include, the fdkim1 and fdkim2 DKIM CNAMEs, why the Return-Path means SPF will not align, and how to reach DMARC enforcement on support email without breaking ticket replies.
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DANE and TLSA records explained
DANE pins your mail server's certificate in DNSSEC-signed TLSA records so senders refuse to deliver over a downgraded or substituted TLS connection. Here is how TLSA records work, how DNSSEC anchors the trust, how DANE compares with MTA-STS, and which one fits your domain.
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Email authentication for government
Public-sector domains are prime spoofing targets because the state's authority is the most valuable brand a fraudster can wear. Here is why government email is forged, the mandates pushing departments to p=reject, and the engineering realities of getting a sprawling government estate to enforcement without cutting off citizen mail.
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What is DKIM and how does it work?
DKIM attaches a cryptographic signature to every message you send, letting receivers verify with a public key in DNS that the mail really came from your domain and was not altered. Learn how signing and verification work step by step, how to read the headers and DNS record, and why a DKIM signature survives forwarding that breaks SPF outright.
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Email authentication for healthcare and HIPAA
HIPAA never names DMARC, but it asks for exactly what SPF, DKIM and DMARC deliver: protection of transmitted PHI, integrity, sender authentication and ongoing risk management. Here is how email authentication maps onto the HIPAA Security Rule, why DMARC reporting need not expose PHI, and the staged path to p=reject that does not break clinical email.
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What is DMARC and how does it work?
DMARC is the control that stops exact-domain spoofing. Here is what it is, how it builds on SPF and DKIM through alignment, what each policy value instructs receivers to do, and how to reach p=reject safely.
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Email authentication for HubSpot: SPF, DKIM and DMARC
A HubSpot-specific guide to email authentication: the exact SPF include, HubSpot's two CNAME-based DKIM selectors, the custom bounce subdomain for return-path alignment, and how to take a HubSpot-sending domain from p=none to p=reject without breaking email.
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What is MTA-STS and how does it work?
MTA-STS forces encrypted, authenticated delivery of your inbound mail. Learn how the _mta-sts DNS record and the HTTPS-hosted policy file work together, the difference between testing and enforce mode, and exactly how it stops TLS downgrade and interception attacks.
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Email authentication for Intercom: SPF, DKIM and DMARC
Intercom gives you both halves of DMARC: a DKIM CNAME and a custom return-path CNAME that makes SPF align. Here is the exact selector, the two records to publish, why you do not add an SPF include, and how to reach p=reject without breaking your onboarding, campaign or support email.
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What is SPF and how does it work?
SPF lets you publish, in DNS, the list of servers allowed to send mail for your domain. Here is how the syntax works, what the all qualifier and each mechanism mean, what SPF actually authorises, the ten-lookup limit that catches everyone, and the spoofing gap that DMARC alignment closes.
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Email authentication for Klaviyo: SPF, DKIM and DMARC
A Klaviyo-specific guide to SPF, DKIM and DMARC: the exact _spf.klaviyomail.com include, the kl/kl2 DKIM selectors, the dedicated sending domain CNAMEs, custom return-path alignment, and the safe path from p=none to p=reject without losing a campaign or flow.
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What is TLS-RPT?
TLS-RPT (SMTP TLS Reporting) is a single safe-to-publish DNS record that gives you a daily, machine-readable summary of how other mail servers negotiated encryption with your inbound MX hosts. Learn what the record and its JSON reports contain, how to decode each failure type, and the exact publish-then-enforce workflow that pairs it with MTA-STS without risking an email outage.
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Email authentication for law firms
How solicitors use SPF, DKIM and DMARC to stop their domain being spoofed, protect client money on completions, and meet their confidentiality duties, with a staged, no-outage path to p=reject.
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Why legitimate email lands in spam
Real, useful email ends up in the junk folder when its signals look untrustworthy to mailbox providers. This guide breaks misfiled mail into its four root causes (authentication, reputation, content and complaints) and shows how to diagnose and fix each with concrete tools and steps, starting with the highest-leverage fix: authentication.
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Email authentication for Mailchimp: SPF, DKIM and DMARC
A Mailchimp-specific guide to SPF, DKIM and DMARC: the exact mcsv.net include, how to publish Mailchimp's DKIM CNAMEs, why default bounce addresses break SPF alignment, and how to reach p=reject without losing a campaign.
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Email authentication for Mailgun: SPF, DKIM and DMARC
A complete, Mailgun-specific walkthrough: the exact SPF include, how to enable and publish DKIM with Mailgun's real selector, why the default return-path breaks SPF alignment, and how to reach DMARC enforcement when sending through Mailgun's subdomain model without an email outage.
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Email authentication for Mailjet: SPF, DKIM and DMARC
A Mailjet-specific guide to SPF, DKIM and DMARC: the exact spf.mailjet.com include and why you can skip it, the mailjet._domainkey DKIM record, why the bnc3.mailjet.com return-path breaks SPF alignment, how to set a custom return-path, and the staged path to p=reject without losing mail.
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Email authentication for Mimecast: SPF, DKIM and DMARC
A Mimecast-specific guide to SPF, DKIM and DMARC: the exact regional includes, generating and publishing a DKIM key from the console, why return-path and From alignment behave differently behind a gateway, and how to reach p=reject without an email outage.
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Email authentication for nonprofits
For charities, DMARC is donor trust and fundraising revenue expressed as DNS records: it stops attackers spoofing your appeals and lifts your own appeals out of the spam folder. Here is how to align every sender, ramp safely to p=reject, and put your logo in the inbox, including via a Common Mark Certificate when your charity logo is not a registered trademark.
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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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