The email deliverability blog
Practical, plain language guidance on sender reputation, authentication, and what it really takes to reach the inbox.
50 articles and countingAll articles
Transactional Email Deliverability: Why Speed, Isolation, and Trust Matter More Than Anywhere Else
A password reset that arrives 30 seconds late is a support ticket. A receipt in spam is a lost customer. Transactional email has the highest stakes and the strictest requirements of any mail you send. Here is how to get it right.
Read articleHow to Read DMARC Reports: A Practical Guide to RUA Aggregate XML and Reaching p=reject
DMARC reports arrive as cryptic daily XML files, and most senders ignore them. Here is how to read the aggregate report, map every sending source, and use the data to reach p=reject without blocking your own mail.
Read moreEmail Sunset Policy and Re-Engagement: How to Win Back Dormant Subscribers Before You Remove Them
Every inactive subscriber quietly drags down your Sender Reputation. Here is how to build a sunset policy with a re-engagement sequence that recovers the winnable contacts and cleanly retires the rest.
Read moreGmail Promotions Tab vs Primary Inbox: How Placement Actually Works and When to Fight It
Landing in the Promotions tab is not a deliverability failure, and chasing Primary placement is often the wrong goal. Here is how Gmail decides tab placement and what actually matters.
Read moreEmail Subdomain vs Separate Domain: The Reputation Isolation Decision for Marketing, Transactional, and Cold Mail
Subdomains give partial reputation isolation, separate domains give full isolation, and choosing wrong either exposes your main domain to risk or wastes months rebuilding reputation. Here is the decision framework.
Read moreThe Email Deliverability Monitoring Cadence: What to Check Daily, Weekly, and Monthly to Catch Problems Early
Your ESP says 99% delivered while a third of your mail sits in spam. Here is the exact daily, weekly, and monthly monitoring routine that catches deliverability problems while you still have time to fix them.
Read moreEmail IP Pool Strategy: How to Segment, Warm, and Manage Sending Pools for Maximum Deliverability
Splitting your mail across the wrong IP pools can quietly starve every pool of the volume it needs to build reputation. Here is how to segment, warm, and manage sending pools correctly in 2026.
Read moreThe Email Authentication Stack Explained: How SPF, DKIM, DMARC, ARC, BIMI, and MTA-STS Fit Together
Six protocols, one system. Here is the complete mental model of how every email authentication layer interlocks, what each one actually does, and the exact order to deploy them.
Read moreWhy Email Open Rates Are Broken in 2026: What MPP, Proxy Caching, and AI Bots Did to Your Metrics
Roughly half of your reported opens are machines, not people. Here is exactly what broke email open rates, how much your dashboard is inflated, and the metrics that actually tell you whether email is working.
Read moreSMTP Error and Enhanced Status Code Reference: The Complete 2026 Guide Including New Enforcement Codes
Every SMTP response code, every enhanced status code, and the new bulk sender enforcement codes Gmail, Yahoo, and Microsoft introduced in 2024 and 2025, in one complete reference with fixes for each.
Read moreAutomated Bounce Handling: How to Build a Bounce Processing Pipeline That Protects Sender Reputation
Ignoring bounces is the fastest way to destroy Sender Reputation. Here is how to build an automated pipeline that parses bounce notifications, classifies them correctly, and suppresses bad addresses before they hurt you.
Read moreGmail Manage Subscriptions: Why High-Frequency Senders Are Getting Pruned and How to Avoid the List
Gmail now shows every user a ranked list of who emails them most, with one-click unsubscribe. If you send too often, you are at the top of that list. Here is how the feature works and how to stay off it.
Read moreVMC vs CMC: Which BIMI Certificate Your Brand Actually Needs in 2026
Gmail now accepts two certificate types for BIMI logos, and the choice between them comes down to trademark ownership, budget, and how badly you want the blue checkmark. Here is the complete decision framework.
Read moreCustom Tracking Domains: Why Default ESP Links Are Quietly Killing Your Click-Through Rates
Every link in your email gets rewritten by your ESP to a shared tracking domain. That shared domain is being blocked, blacklisted, and stripped by corporate filters in 2026. Here is the complete fix.
Read moreDANE and TLSA Records for Email: The Advanced Transport Security Layer Beyond MTA-STS
DANE uses DNSSEC to pin TLS certificates directly in DNS, eliminating reliance on certificate authorities. Here is how DANE actually works for SMTP, how to deploy TLSA records, and why Microsoft enabled DANE in 2026.
Read moreSalesforce Marketing Cloud and Pardot Deliverability: The Complete Authentication and Configuration Guide
Salesforce sends email through three different products with three different authentication models. Here is exactly how to configure deliverability across core Salesforce, Account Engagement (Pardot), and Marketing Cloud in 2026.
Read moreB2B Email Deliverability: How Corporate Inboxes Filter Differently from Consumer Email
B2B mail crosses 3-7 additional filtering layers that B2C senders never see. Here is how Microsoft Defender, Proofpoint, Mimecast, and corporate gateways actually filter, and what B2B senders need to do differently.
Read moreEmail Forwarding and Authentication: Why SPF Breaks and How SRS and ARC Save Your Mail
Every email forward breaks SPF by design. Here is exactly why forwarded mail fails authentication, how Sender Rewriting Scheme fixes SPF but breaks DMARC, and how ARC completes the chain.
Read moreRFC 8058 One-Click Unsubscribe: The Complete Technical Implementation Guide for Bulk Senders
Gmail and Yahoo now reject bulk mail without working one-click unsubscribe. Here is the exact RFC 8058 implementation, from headers to server-side handling to common bugs that silently break compliance.
Read moreCase Study: How a Shopify Store Recovered From a Black Friday Spam Trap Disaster
A $4M Shopify brand imported a "Black Friday deals subscriber" list, hit 340 spam traps, landed on Spamhaus CSS, and lost 71% of email revenue overnight. The complete recovery sequence.
Read moreiCloud and Apple Mail Deliverability: The Complete Sender's Guide for 2026
iCloud filters differently than Gmail and Outlook, with no postmaster tools and stricter authentication enforcement. The complete guide to landing in Apple inboxes consistently.
Read moreEmail Frequency: How Often to Send Without Damaging Sender Reputation
Send frequency directly affects complaint rates, engagement, and inbox placement. The complete decision framework for finding the right cadence for your audience and content.
Read moreDKIM Replay Attacks: How Spammers Exploit Valid Signatures and How to Stop Them
DKIM replay attacks let spammers borrow valid signatures from trusted senders to launder spam through legitimate domain reputation. The complete technical guide to detection and defense.
Read moreCase Study: How a B2B SaaS Cut Spam Folder Placement From 60% to 4% in 90 Days
A real recovery playbook from a 50-person SaaS company that watched trial conversions collapse when their lifecycle emails started landing in spam. The exact diagnosis, fixes, and timeline.
Read moreEmail Warmup Services in 2026: The Truth About Mailwarm, Lemwarm, and Warmup Inbox
Email warmup services promise to build sender reputation automatically, but Google and Microsoft are actively detecting and terminating accounts. The complete 2026 reality check.
Read moreHubSpot Email Deliverability: The Complete Guide to Inbox Placement in 2026
HubSpot sends through shared and dedicated IP pools, with deliverability shaped heavily by your connected domain setup. The complete configuration and operational playbook for HubSpot senders.
Read moreEmail Spam Trigger Words in 2026: What Actually Triggers Filters (and What Does Not)
The classic spam word lists are mostly wrong. Here is what modern email filters actually evaluate, which words still matter, and the patterns that hurt deliverability more than any single word.
Read moreCASL Compliance: The Complete Guide to Canada's Anti-Spam Law for Email Senders
CASL is the strictest commercial email law in North America, with penalties up to $10M per violation. Learn the consent rules, required elements, and how CASL compares to CAN-SPAM and GDPR.
Read moreHow to Remove Your Domain or IP From Email Blacklists: Spamhaus, Barracuda, and Beyond
A step-by-step removal guide for the major email blacklists. Learn how delisting works on Spamhaus SBL, CSS, PBL, Barracuda, SORBS, SpamCop, and how to stay off.
Read moreMTA-STS and TLS-RPT: The Complete Email Transport Security Setup Guide for 2026
MTA-STS prevents downgrade attacks on inbound email by enforcing TLS encryption. Learn how to deploy MTA-STS policies and TLS-RPT reporting in 2026.
Read moreEmail Tracking Pixels: How They Work, Privacy Impact, and Modern Alternatives
Email tracking pixels measure opens by loading invisible images, but Apple Mail Privacy Protection and modern email clients have changed what tracking actually reveals. Learn how pixels work and what to track instead.
Read moreMailchimp Deliverability: The Complete Guide to Inbox Placement on Mailchimp
Mailchimp powers email for over 11 million businesses but inbox placement is not automatic. Learn how Mailchimp's shared IP pools, Omnivore abuse system, and authentication setup affect your deliverability.
Read moreARC Email Authentication Explained: How Authenticated Received Chain Saves Forwarded Mail
Authenticated Received Chain (ARC) preserves SPF and DKIM results across forwarders and mailing lists. Learn how the three ARC headers work, who needs to sign, and how Gmail, Microsoft, and Yahoo handle ARC chains.
Read moreShared vs Dedicated IP for Email Sending: The 2026 Decision Framework
The shared vs dedicated IP question is not about volume or prestige. Here is the actual framework that determines which choice gives you better deliverability, with the real costs and tradeoffs.
Read moreIPv6 Email Sending: Why It Matters, When to Enable It, and How to Avoid Deliverability Disasters
IPv6 is quietly becoming the default for outbound email at major providers, and misconfigured IPv6 sending is silently destroying deliverability. Here is what actually works in 2026.
Read moreMicrosoft Outlook Bulk Sender Enforcement 2026: What Changed and How to Stay Delivered
Microsoft reached full enforcement of bulk sender requirements in late 2025 and tightened further in 2026. Here is exactly what is being rejected, why, and how to get compliant before your business mail starts silently disappearing.
Read morePTR Records and Reverse DNS: The Complete Email Deliverability Setup Guide for 2026
Missing or misconfigured PTR records are quietly rejecting legitimate business email in 2026. Here is exactly how reverse DNS works, why Gmail and Microsoft now enforce it, and how to configure it correctly.
Read moreBest Bulk Email Services in 2026: SendGrid, Brevo, Amazon SES, Mailgun, and Postmark Compared
An in-depth comparison of the five most popular bulk email services for 2026, covering deliverability, pricing, features, and the exact use case each one wins.
Read moreEmail Verification APIs: How Real-Time Signup Validation Protects Sender Reputation
A technical guide to real-time email verification APIs: how they work, what they catch, and why point-of-capture validation is the most effective deliverability defense for senders in 2026.
Read moreYahoo Mail 15GB Storage Cap: What the New Mailbox Limit Means for Email Senders in 2026
Yahoo began enforcing a 15GB storage cap on free Yahoo Mail accounts in 2025, expanding globally in 2026. A complete analysis of the sender impact, bounce patterns, and list hygiene strategy shifts this change forces.
Read moreAmazon SES Deliverability: Authentication, Custom MAIL FROM, and Production Configuration
Complete Amazon SES deliverability guide: Easy DKIM CNAMEs, Custom MAIL FROM for SPF alignment, sandbox-to-production transition, DMARC policy progression, and the "via amazonses.com" warning explained.
Read moreShopify and Klaviyo Deliverability: The Complete Ecommerce Sender Playbook for 2026
How Shopify stores using Klaviyo can fix Promotions tab placement, resolve unverified sender warnings, configure DKIM correctly, and protect sender reputation through the ecommerce sending cycle.
Read moreMicrosoft 365 SPF, DKIM, and DMARC: The Complete 2026 Setup Guide
Step-by-step authentication configuration for Microsoft 365 and Office 365, including the May 2025 Outlook bulk sender requirements, DKIM CNAME troubleshooting, and enforcement progression.
Read moreAI Email Agents Are a Deliverability Disaster Waiting to Happen: What Sender Reputation Teams Need to Know Now
AI agents can now provision their own email infrastructure and send autonomously. A comprehensive analysis of the sender reputation risks, the OpenClaw incident, and the guardrails that actually prevent agent-driven reputation collapse.
Read moreGoogle Workspace SPF, DKIM, and DMARC: The Complete 2026 Setup Guide
Step-by-step configuration of SPF, DKIM, and DMARC for Google Workspace with 2026 bulk sender compliance, Cloudflare gotchas, and the enforcement progression most admins miss.
Read moreNewsletter Sender Reputation: How Creators and Publishers Win Deliverability in the Substack, Beehiiv, and Kit Era
Publishers sent 28 billion newsletter emails in 2025 reaching 255 million readers. A complete sender reputation framework for creators running on Substack, Beehiiv, Kit, Ghost, and ConvertKit.
Read moreLookalike Domain Defense: Stopping Typosquatting, Homograph, and AI-Generated Impersonation Attacks on Your Brand
80% of domains resembling Global 2000 brands are owned by third parties and 42% are configured to send email. A defensive framework for detecting, responding to, and preventing lookalike domain attacks.
Read moreESP Migration Without Destroying Your Sender Reputation: The Complete Transition Playbook
Switching email service providers can wipe out years of sender reputation in weeks if the transition is mishandled. A complete playbook for migrating ESPs while protecting deliverability from day one.
Read moreAI-Generated Phishing: Why Sender Authentication Is the Last Line of Defense in 2026
82.6% of phishing emails are now AI-generated, and traditional content-based filters are failing. Why cryptographic sender authentication has become the defining defensive layer against the new threat landscape.
Read moreThe State of Email Authentication 2026: Why 778,000 Domains Published DMARC Records but Never Enabled Protection
A data-driven analysis of DMARC adoption across 5.5 million domains reveals a critical gap. Publication has grown sharply since 2024, but actual enforcement lags far behind, leaving the majority of authenticated domains still vulnerable to spoofing.
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