Deliverability insights
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Yahoo Spam Filter: How It Differs From Gmail and What Senders Must Know
Yahoo is still 8% of US B2C recipients. Its complaint loop, its IP-level reputation weighting, and the three things Yahoo punishes that Gmail doesn't.
How to Automate Inbox Placement Tests With AI Agents (MCP + Claude)
Give Claude Desktop or Cursor the Inbox Check MCP server and let the agent run tests, diagnose placement, and propose DNS fixes on its own.
How to Set Up DKIM and SPF for Microsoft 365
Defender → Email & collaboration → Policies & rules → Email authentication settings. Every click, plus the CNAME gotchas that trip up admins.
BIMI: How to Show Your Logo in Gmail and Yahoo Inbox
A full BIMI rollout — SVG Tiny PS, VMC, DMARC p=quarantine prerequisite — plus whether the $1,500 VMC is actually worth it for your brand.
SPF Too Many Lookups: How to Fix the 10-Lookup Limit
Why SPF flattening is half a solution, how to audit your lookup count, and the cleanest fix — dedicated subdomains per vendor.
Mailchimp Deliverability: Why Your Campaigns Land in Spam
Shared IPs, free-tier senders, "via mailchimp.com" in your headers. The Mailchimp-specific reputation problems and how to work around them.
Tracking Pixels in Cold Email: Do They Help or Hurt Deliverability?
The data behind image-trackers. Why a 1×1 gif correlates with 12% lower Gmail inboxing — and when it's still worth the hit.
HubSpot Email Deliverability: How to Test Before You Send
HubSpot's own "Sent" metric isn't inbox placement. A quick pre-send loop that adds real placement data to your HubSpot workflow.
ProtonMail, iCloud, Zoho, Fastmail: How Privacy-First Providers Filter Your Email
They're smaller but their users are harder to convert. How privacy-first ISPs rank your mail and the three things that get you into their inboxes.
Woodpecker vs Lemlist vs Instantly: Deliverability Compared
We ran the same 100-email campaign through all three. Inbox rates, warm-up behaviour, and where each tool silently hurts deliverability.
Google Postmaster Tools: How to Read Your Domain Reputation
The only honest window into how Gmail sees you. What each metric means, what "Medium" reputation actually costs you, and how to move each needle.
Custom Tracking Domain: Why You Need One and How to Set It Up
Default shared tracking domains are often blacklisted. How to set up a CNAME-based custom tracking domain in Lemlist, Instantly and HubSpot.
The Most Common SPF/DKIM/DMARC Errors (Based on 1,000 Tests)
We analysed 1,000 real deliverability tests. The seven authentication errors that show up over and over — and the exact record fix for each.
SpamAssassin Score: What It Means and How to Lower It
What each SpamAssassin rule is testing, why HTML/text ratio trips honest senders, and how to go from 8.1 to 0.9 without rewriting your template.
Building an Email Deliverability Monitor With Our API (Developer Guide)
A 30-minute walk-through: Bearer auth, scheduled tests, SSE result streaming, and a Slack alert when a sender's inbox rate drops below 80%.
Shared IP vs Dedicated IP for Email: Which Is Better?
When to pay for a dedicated IP, when shared-IP pools are actually better, and the volume threshold where the answer flips.
Inbox Placement Rates by Industry: Who Gets to Inbox and Who Doesn't
SaaS, e-commerce, crypto, recruiting, financial services. Median inbox rates per industry and why the bottom two industries get filtered harder.