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Email Deliverability Guides & Best Practices
Guides, best practices, and intelligence from the InboxEagle team to help you land in the inbox every time.
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Does DMARC Failure Guarantee the Spam Folder? A 2M Email Study
We analyzed 2.2 million emails to find out if DMARC failure sends you straight to spam. The answer is more nuanced — and more actionable — than you'd expect.
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Email Blacklists: What They Are, How You Get Listed, and How to Get Off (2026)
An email blacklist can silently block your campaigns before a single recipient sees them. Here's what blacklists are, the exact behaviors that trigger a listing, how to run a free email blacklist check, and how to get removed.
Do Spam Trigger Words Really Cause Spam? 774K Emails Tested
Do spam trigger words like 'free' and 'sale' actually send emails to spam? We analyzed 774,828 emails from Q1 2026. The findings may surprise you.
How to Check Your Email Sender Reputation Score
Your sender reputation score determines inbox or spam — before you hit send. Here's how to check it for free across Gmail, Outlook, and enterprise infrastructure, and what to do when the numbers are bad.
Email Sunset Policy: The Data Behind a 3× Spam Rate Gap
InboxEagle analyzed 16,356 ecommerce senders. Low-volume programs average a 56% spam rate. High-volume programs average 18%. The difference is a sunset policy.
Klaviyo Suppression Lists: How to Use Them to Protect Deliverability
Klaviyo suppression list: five suppression types, global vs. list-level scope, what can be reversed, the billing distinction most brands miss, and how to use it to actively protect inbox placement.
Email Authentication for Klaviyo Senders: The Complete Guide
Email authentication is the foundation of inbox placement for every Klaviyo sender. Here's what SPF, DKIM, and DMARC actually do, why Klaviyo's default setup breaks DMARC alignment, and where to go deeper on each.
Email Deliverability for Agencies: How to Manage Multiple Client Domains
Managing email deliverability across multiple client domains is one of the hardest operational challenges in eCommerce agency work. Here's the framework — domain isolation, monitoring at scale, and the mistakes that cause one client to hurt another.
Email List Hygiene: The Deliverability Practice Most eCommerce Brands Skip
Email list hygiene is one of the highest-leverage deliverability practices for eCommerce brands — yet most skip it until a crisis forces their hand. Here's exactly what it is, why it matters, and how to diagnose and fix list decay in Klaviyo.
Why Your "Mailed-By" Domain Matters for Brand Trust
82.8% of marketing emails display a third-party mailed-by domain in Gmail. Here's what that signals to your subscribers and why it's quietly costing you deliverability equity.
How to Monitor Your Email Deliverability in Real Time
A practical guide to email deliverability monitoring in real time — the signals that matter, the tools that surface them, and how to act before a problem becomes a crisis.
List-Unsubscribe Header: Does It Actually Reduce Spam Rates?
Does the List-Unsubscribe header actually lower spam rates? InboxEagle's study of 19,797 brands reveals a 4.86x extreme spam risk for senders without it.
Setting Up a Custom Sending Domain in Klaviyo: Step by Step
A complete guide to setting up a Klaviyo custom sending domain — with DNS records, authentication verification, and why it matters for deliverability.
MTA-STS and TLS-RPT: The Email Security Standards Most Brands Miss
SPF, DKIM, and DMARC get all the attention — but MTA-STS and TLS-RPT are the two DNS records that complete your domain's email security posture. Here's what they do, why they matter, and how to set them up.
The Technical Anatomy of a Perfect Ecommerce Email Header
InboxEagle analyzed 256,606 emails across 16,381 brands. Only 16.7% had a perfect header. Here's what separates them from the rest — and how to fix yours.
The Correlation Between High Sending Frequency & Spam Complaints
Does sending more emails mean more spam complaints? InboxEagle analyzed 31,586 sending programs — the data tells a more nuanced story than you think.
Gmail Spam Rate Thresholds: What 0.10% and 0.30% Actually Mean for You
Gmail enforces two spam rate thresholds that most senders misread. Here's exactly what 0.10% and 0.30% mean, how they're measured, and what to do before you breach either one.
12 Email Marketing Mistakes Killing Your Deliverability in 2026
Sending but not landing? These 12 email marketing mistakes — from skipped authentication to bought lists — are the most common reasons emails go to spam. Learn what to fix.
What Is a Sending Domain and Why Does It Need Its Own Reputation?
Your sending domain is the identity your email program lives or dies by — and it's separate from your website. Here's what it is, why it needs its own reputation, and what most Klaviyo senders get wrong about it.
Email Domain Reputation: How It's Scored and How to Protect It
Email domain reputation is the primary signal ISPs use to route your campaigns. Here's exactly how it's scored, what damages it fastest, and how to protect it before the next send.
Data Study: How Spam Rates Affect Your Gmail Promotions Placement
We bucketed 671,329 emails by spam complaint rate and tracked where they landed in Gmail. The findings reveal a hard cliff — and show exactly what it takes to protect your sender reputation.
Dedicated IP vs. Shared IP for Email: What the Data Actually Shows
InboxEagle analyzed 15,174 IPs — 7,166 dedicated and 8,008 shared. Dedicated IPs had lower spam rates but lower Primary inbox. Here's why, and when a dedicated IP for email actually makes sense.
How Domain Alignment Affects Inbox Placement in 2026
Domain alignment is why your emails fail DMARC even with valid SPF and DKIM — here's what's breaking and how to fix it.
The State of Email Authentication: SPF/DKIM Adoption in Ecommerce
Email authentication adoption in ecommerce leads every other industry — yet most brands still run DMARC at p=none. Here's what the 2025/2026 data says and where the real gap is.
Gmail Deliverability Benchmarks for Ecommerce Brands: Q1 2026 Data
InboxEagle monitored 721,351 emails to Gmail in Q1 2026. Here are the real gmail deliverability benchmarks — spam rates, tab placement, and what separates healthy programs from at-risk ones.
The Ecommerce Email Deliverability Gap: What Top Brands Do Differently
InboxEagle analyzed 3,474 ecommerce sender domains and found a 72-point inbox placement gap between the best and worst performers. Here's the ecommerce email performance benchmark — and what separates top-quartile brands from everyone else.
Do Aggressive Sale Subject Lines Hurt Deliverability? What Our Data Shows
Sale language doesn't automatically hurt deliverability — but some patterns do. InboxEagle analyzed 721,351 emails and found results that flip conventional wisdom on its head.
BIMI in 2026: Google's CMC Makes Brand Logos Affordable for Everyone
Google launched a Common Mark Certificate option for BIMI in 2025 — no trademark required. Here's how BIMI works, what's changed, and whether it's worth implementing for your email program.
Microsoft Outlook's Bulk Sender Requirements: What Email Marketers Need to Know
Microsoft began enforcing bulk sender requirements for Outlook, Hotmail, and Live.com on May 5, 2025. Non-compliant mail gets a 550 5.7.515 rejection. Here's exactly what's required and how to comply.
Ecommerce Email Benchmarks 2026: Inbox, Promotions & Spam
InboxEagle analyzed 721,351 ecommerce emails in Q1 2026. Here's where they landed — Primary, Promotions, and Spam — and what the data means for your sending program.
Where Your Email Lands: Inbox, Promotions, or Spam?
Most senders track delivered vs. spam. But Gmail has a third folder — the Promotions tab — that quietly buries marketing emails just as effectively. Here's what determines where your email lands, and how to see all three outcomes before you send.
Email Deliverability Checklist: 30 Pre-Send Checks
A complete pre-send checklist covering authentication, sender reputation, list hygiene, content, and monitoring — updated for 2026 enforcement requirements.
How Email Spam Filters Work: What ISPs Check Before Delivering Your Email
A technical but accessible explanation of how Gmail, Outlook, and Yahoo decide whether your email reaches the inbox or the spam folder.
How AI Monitors Email Deliverability: What's Actually Different
AI-powered deliverability monitoring alerts you in under 1 minute, identifies root causes, and generates action plans — here's exactly how it works differently from traditional dashboards.
What Is a Good Inbox Placement Rate? 2026 Benchmarks
Industry benchmarks for inbox placement rates across eCommerce, SaaS, and B2B — and what to do if yours falls short.
Inbox Placement vs. Delivery Rate: Know the Difference
Your ESP says 99% delivered. But how much of that mail actually reached the inbox? The difference between delivery rate and inbox placement rate — and why it matters enormously for revenue.
Why Your Email Open Rate Is Lying to You (And What to Track Instead)
Apple Mail Privacy Protection and security scanner pre-fetching have made open rate an unreliable metric. Here's what's happening, why high open rates can be a warning sign, and what to measure instead.
Why Your Welcome Series Is the Most Dangerous Flow for Sender Reputation
Open rates look great in week one — but your domain reputation may already be tanking. Here's what's really happening inside your welcome series and how to fix it.
Win-Back Campaigns: The Right Way to Re-engage Without Destroying Your Reputation
Most win-back campaigns are run wrong — mailing too many inactive subscribers, skipping seed tests, and never actually sunsetting non-responders. Here's how to do it correctly.
Managing Email Sender Reputation During E-commerce Volume Spikes
How to protect your inbox placement during Black Friday, product launches, and other high-volume sending events.
Google Postmaster Tools v2: The Complete Setup and Interpretation Guide
How to set up Google Postmaster Tools v2, understand the new Compliance Dashboard, and what replaced the retired reputation scores.
Fixing Inbox Placement Issues in Klaviyo: A Practical Guide
Step-by-step troubleshooting for Klaviyo users struggling with spam placement, low open rates, and sender reputation issues.
SPF, DKIM, and DMARC Explained: The Authentication Trinity
A plain-English breakdown of the three email authentication standards every sender needs — plus who enforces them and what comes next.
The Complete Email Deliverability Guide for 2026
Everything you need to know about landing in the inbox — from authentication to reputation management, updated for 2026 enforcement changes.