Metrics and Benchmarks
Inbox Placement Rate vs Delivery Rate
Your delivery rate says 99% and a quarter of your email is in spam. Those are different numbers, and only one of them describes whether anyone saw your campaign.
Oct 16, 20265 min read
Tag
#email deliverability
12 articles tagged with email deliverability.
Design and Accessibility
The Pre-Send Email Testing Checklist
The five minutes before you press send are the cheapest quality control in marketing. This is the checklist, in the order that catches the most problems soonest.
Oct 14, 20265 min read
Compliance and Privacy
Double Opt-In vs Single Opt-In
Double opt-in costs you a fifth of your signups and buys you a cleaner list, better deliverability and proof of consent. Here is when the trade is worth it.
Oct 7, 20265 min read
Compliance and Privacy
The List-Unsubscribe Header, Explained
The List-Unsubscribe header is what puts the unsubscribe link next to your name in Gmail. It is now required for bulk senders, and it protects you from spam complaints.
Sep 25, 20265 min read
Compliance and Privacy
Google and Yahoo Bulk Sender Requirements
Since February 2024 Google and Yahoo enforce authentication, one-click unsubscribe and a spam complaint ceiling. Here is exactly what they check and how to pass.
Sep 19, 20265 min read
Deliverability
Sender Reputation: What It Is & How to Improve It
Sender reputation decides whether your email reaches the inbox. This guide breaks down the signals mailbox providers actually score, the difference between domain and IP reputation, healthy benchmark ranges for complaints and bounces, seven habits that build reputation, and a step-by-step recovery plan when it drops.
Aug 24, 20269 min read
Deliverability
Best Email Deliverability Testing Tools (2026)
Deliverability is five separate problems, and each needs a different tool. This guide breaks down authentication checkers, blocklist monitors, seed-list placement testers, spam scorers, and DMARC analyzers, with a comparison table, a dependency-ordered audit sequence, and the metrics that prove it is working.
Aug 23, 20269 min read
Transactional & SMTP
SMTP Error Codes Explained (and How to Fix Them)
A practical reference for SMTP error codes: how to read a reply in ten seconds, the difference between 4xx soft bounces and 5xx hard bounces, lookup tables for the codes you will actually hit, and fixes for the five that cause most real-world pain — plus the ports that quietly cause silent failures.
Aug 16, 20269 min read
Transactional & SMTP
Transactional Email Templates + Examples
The nine transactional email templates every product needs, with copy examples for password resets, receipts, failed payments, and shipping notices. Includes a transactional vs. marketing comparison table, sending-stream separation advice, variable-naming rules, and a pre-launch QA checklist.
Aug 15, 20269 min read
Transactional & SMTP
Best Email APIs Compared (2026)
How to choose the best email API in 2026 without getting lost in feature checklists. Covers the eight evaluation criteria that actually predict deliverability, the four categories providers fall into and their tradeoffs, how to read API docs like an engineer, a REST-versus-SMTP comparison table, and a safe migration sequence.
Aug 14, 20269 min read
Deliverability
Email Spam Trigger Words to Avoid (2026 List)
A practical 2026 list of email spam trigger words, the formatting habits that amplify them, and the phrases that are actually safe. Includes rewrite examples and a pre-send checklist.
Aug 4, 20268 min read
Email Copywriting
Best Cold Email Subject Lines (+ Formulas)
Proven cold email subject lines that read like a real person -- personalized, question-based, curiosity, and social-proof lines -- plus copy-ready formulas and the deliverability rules that keep them out of spam.
Jul 19, 20269 min read