FeaturedBest Practices
How to Monitor Email Deliverability: What to Check and How Often
How to monitor email deliverability: the signals to watch, the Gmail, Yahoo and Microsoft thresholds, how often to check each one, and a simple weekly routine.
Blog
Formula Inbox is your resource for all things email deliverability.
Best Practices
What Does an Email Deliverability Audit Include?
What a real email deliverability audit checks, from SPF, DKIM and DMARC to reputation, blacklists and inbox placement, and how to run a basic one your…
Advice
Validity's Heatwave Blocklist: What It Means If You Use Email Warm-Up
Validity's Heatwave blocklist flags domains built on warm-up networks, and stopping does not clear a listing. Learn how to check and what to do next.
Regulations
Cold Email Is Legal. Most Cold Programs Still Break CAN-SPAM.
CAN-SPAM is opt-out, so cold email is legal. But most cold programs quietly break it. Here's where compliance fails and what a clean setup looks like.
Advice
Deliverability Consultant vs. Deliverability Software: Which One Do You Actually Need?
Software tells you where your email stands. A consultant fixes why it's failing. Here's what each one does, and where the tools quietly stop helping.
Tools
Spam Testing Tools Compared: mail-tester, Unspam, MailChecker, Postbox Mailtester and Formula Inbox
mail-tester, Unspam, MailChecker, Postbox Mailtester and the Formula Inbox assessment compared: what each checks, where it stops, and when to use it.
Advice
Why Your Email Open Rates Are Dropping and Whether It Is a Deliverability Problem
Open rates dropping? It might be deliverability, or it might be something else. This guide shows how to tell the difference and fix the actual problem…
Advice
Email Deliverability vs Email Marketing: What Is the Difference and Why Does It Matter?
Email deliverability and email marketing are not the same thing. Learn the difference and why better campaigns cannot fix an inbox placement problem.
Advice
What Is BIMI and How Do You Set It Up? The Complete Email Logo in Inbox Guide for 2026
BIMI shows your logo next to your emails in Gmail, Yahoo and Apple Mail. Learn the DMARC, logo and certificate requirements and how to set it up.
Advice
Email Deliverability Metrics: The 8 Numbers That Actually Tell You If Your Emails Are Working
Most email marketers track the wrong metrics. These 8 deliverability numbers show whether your emails reach the inbox, with 2026 benchmarks for each.
Expert Email
Deliverability Managers
Our highly experienced email deliverability managers uncover and resolve the issues that keep messages from their intended recipients. After a full audit and remediation, Formula Inbox clients see inbox placement rates above 90%, based on seed list tests that reflect their ideal customer profile. Are you ready to do the same?