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Deliverability, demystified.
Field-tested guides on email authentication, content quality, and reading your WillItInbox report.
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Agency deliverability audit template
A repeatable audit structure for agencies reviewing client sender domains, templates, lists, DMARC, and monitoring.
Read article- ·1 min read
Mail Tester alternative: when you need API, validation, and monitoring
A practical comparison for teams that need more than a one-off spam score.
AlternativesMail TesterAPI - ·1 min read
Deliverability QA in CI/CD with the WillItInbox API
How developers can turn deliverability testing and validation into repeatable checks around releases, templates, and imports.
APICI/CDDevelopers - ·1 min read
Inbox placement testing: what seed tests can and cannot prove
Seed tests are useful diagnostics, but they do not replace reputation, engagement, and real recipient behavior.
Inbox placementSeed testsDeliverability - ·1 min read
DMARC aggregate reports: finding unknown senders
How to use DMARC aggregate reports to find forgotten SaaS tools, misaligned ESPs, and suspicious sources before moving to enforcement.
DMARCMonitoringAuthentication - ·1 min read
Bulk email validation CSV checklist
A practical checklist for uploading, validating, segmenting, and exporting CSV email lists without damaging sender reputation.
Bulk validationCSVList hygiene - ·1 min read
Email validation API: valid, risky, catch-all, and unknown explained
How to interpret validation API results without treating SMTP evidence as magic certainty.
APIValidationList hygiene - ·1 min read
How to check if your email will go to spam before launch
A launch checklist for testing real messages, sender authentication, DNS, headers, content, links, and recipient quality before a campaign or product email goes live.
DeliverabilityLaunch checklistQA - ·4 min read
The Gmail and Yahoo bulk sender rules: a 2026 checklist
What changed in February 2024, what was tightened in 2025, and the seven requirements you must meet if you send over 5,000 messages a day.
DeliverabilityGmailYahooCompliance - ·4 min read
DKIM key rotation: a safe, zero-downtime playbook
Why rotating DKIM keys matters, when to do it, and the exact two-selector cutover that keeps signatures valid through the change.
DKIMAuthenticationDNS - ·5 min read
SPF record syntax: a complete cheat sheet (with examples)
Every SPF mechanism, qualifier, and modifier — what they mean, when to use them, and the four mistakes that break 90% of records.
SPFAuthenticationDNS - ·4 min read
DMARC rollout: from p=none to p=reject without breaking mail
The exact six-week schedule for moving from monitoring-only DMARC to full enforcement, with the report-reading checkpoints that keep you safe.
DMARCAuthentication - ·3 min read
Understanding SPF, DKIM & DMARC
The three records every sender needs — what they do, how they interact, and how to set them up without breaking your existing mail flow.
AuthenticationDNS - ·4 min read
BIMI explained: putting your logo in the inbox
What BIMI does, what it costs (a VMC), and the four DNS records and SVG constraints you need to ship it.
BIMIAuthenticationBranding - ·3 min read
MTA-STS and TLS-RPT: enforcing TLS for inbound mail
How to require TLS for messages sent to your domain, and how to get reports when receivers can't honor your policy.
TLSMTA-STSAuthentication - ·2 min read
DMARC alignment, explained without the jargon
Why DMARC can pass when SPF fails, why strict alignment exists, and how to read alignment errors in your aggregate reports.
AuthenticationDMARC - ·3 min read
ARC: how forwarded mail still passes DMARC
What Authenticated Received Chain does, who actually uses it, and why mailing lists and forwarders are the only place it matters.
ARCDMARCAuthentication - ·4 min read
DNSSEC for email: when it matters and when it doesn't
What DNSSEC actually protects in your mail flow, the receivers that care, and the ops cost of keeping it healthy.
DNSSECDNSAuthentication - ·2 min read
Why your emails land in spam
Beyond authentication: content patterns, IP reputation, and engagement signals that quietly route legitimate mail to junk folders.
DeliverabilityContent - ·4 min read
Bounces decoded: hard, soft, block, and how to handle each
What every SMTP bounce code actually means, which ones to retry, and the suppression rules that keep your reputation intact.
BouncesDeliverabilitySMTP - ·2 min read
The DNSBL landscape in 2026
Which blacklists actually matter, which ones to ignore, and how to handle a listing without panicking.
ReputationDNS - ·3 min read
Feedback loops (FBLs): how to know when recipients hit 'spam'
Every major receiver's FBL program, how to enroll, and the suppression discipline that turns complaints into long-term placement gains.
FBLDeliverabilityReputation - ·3 min read
IP warming: a 30-day schedule that actually works
The day-by-day volume ramp for warming a new sending IP, the engagement gates between stages, and the three signs you're moving too fast.
IP WarmingReputationDeliverability - ·2 min read
Microsoft SNDS: the deliverability tool nobody reads correctly
Smart Network Data Services exposes the complaint and trap data Outlook.com uses to filter you. Here is what each column means and the thresholds that actually matter.
SNDSMicrosoftOutlookReputation - ·2 min read
Reading your WillItInbox report
A walkthrough of the five score categories, what each check means, and how to prioritise fixes when you have limited time.
Guide - ·2 min read
Image-to-text ratio: the rule that breaks newsletter design
Why image-heavy emails get filtered, the 60/40 rule that mostly works, and how to design beautiful HTML email without triggering content scanners.
HTML EmailSpam FiltersDesign - ·3 min read
PTR records and reverse DNS: the small fix with big impact
Why receivers reject mail from IPs without proper reverse DNS, how PTR records work, and the one-record fix most self-hosters miss.
PTRrDNSInfrastructure - ·2 min read
List-Unsubscribe and one-click unsubscribe: the 2024 requirement
Gmail and Yahoo now require RFC 8058 one-click unsubscribe for bulk senders. Here are both header formats, the POST endpoint contract, and the gotchas that break it.
List-UnsubscribeRFC 8058GmailYahoo - ·2 min read
Return-Path: where bounces actually go and why it matters
The Return-Path header tells receivers where to send bounce notifications. Get it wrong and you go blind to delivery failures. Here is the SPF, DMARC, and bounce-loop interaction.
Return-PathBouncesSPFBounce Handling - ·3 min read
Google Postmaster Tools: a complete walkthrough
Setting up Postmaster Tools, reading every dashboard, and turning the eight metrics into concrete deliverability fixes.
Postmaster ToolsGmailReputation - ·2 min read
Reverse DNS and HELO — the most overlooked deliverability lever
Forward-confirmed reverse DNS is invisible until it's missing, and then it silently kills your mail.
InfrastructureDNS - ·2 min read
DMARC p=quarantine vs p=reject: when to graduate
p=none monitors. p=quarantine warns. p=reject blocks. The decision tree for moving between them and the metrics that tell you it is safe.
DMARCPolicyAuthentication - ·2 min read
Subdomain strategy: why marketing.example.com beats [email protected]
Splitting transactional, marketing, and corporate mail across subdomains protects your most important traffic from your noisiest. Here is the layout that works.
SubdomainsReputationArchitecture - ·3 min read
Blacklist removal: the playbook for Spamhaus, Spamcop, and friends
Which DNSBLs actually matter, how to find your listings, and the exact delisting process for the eight most consequential blocklists.
DNSBLBlacklistReputation - ·2 min read
MX records: priority, fallbacks, and the mistakes that lose mail
MX records tell the world where to send mail addressed to your domain. Misconfigured priorities, missing TTLs, and CNAME traps cause silent loss every day.
MXDNSMail Routing - ·2 min read
Accessible HTML email: structure, contrast, and the screen-reader test
Accessibility and deliverability are quietly the same skill. Semantic structure, alt text, and 4.5:1 contrast help filters as much as they help readers.
AccessibilityHTML EmailDesign - ·3 min read
Plain text vs HTML email: why both matter (and how to ship both)
Why HTML-only emails get filtered, what a clean multipart/alternative looks like, and the four-line MIME structure to copy.
ContentMIMEDeliverability - ·2 min read
Reading your WillItInbox report: every score, every check, every fix
What the overall score means, how the five category scores combine, and how to triage findings from critical to cosmetic.
WillItInboxReportHow-to - ·3 min read
Spam trigger words: what actually scores (and what doesn't)
The myth of the trigger-word list, the small set of phrases that genuinely matter, and how SpamAssassin actually weights content.
ContentSpamAssassinCopywriting - ·2 min read
List-Unsubscribe and one-click headers
Gmail and Yahoo's 2024 bulk-sender requirements made these headers mandatory. Here's how to implement them correctly.
HeadersCompliance - ·3 min read
List hygiene: when to suppress, when to sunset, when to remove
The discipline that separates senders with 30% open rates from senders in spam: validating signups, sunsetting unengaged, and the four suppression categories you must track separately.
List HygieneEngagementDeliverability - ·2 min read
Warming a new sending domain — a realistic 4-week schedule
Day-by-day volume targets, recipient selection, and the warning signs that mean you should slow down.
ReputationOperations - ·2 min read
Reading SpamAssassin rules — and how to defuse the top 20
SpamAssassin's rule corpus is enormous, but a small handful of rules account for most of the points your campaigns lose.
ContentSpamAssassin - ·2 min read
Transactional vs marketing email — separate them or suffer
Why running both streams from the same domain is a deliverability liability and how to split them cleanly.
OperationsReputation