The Deliverable Diary

If your emails are landing in spam, the cause is almost always one of seven things: missing or misconfigured authentication, a damaged sender reputation, a high complaint rate, a dirty or purchased list, a brand-new or cold-warmed domain, a content or link pattern that trips filters, or an SMTP provider that’s quietly making things worse. […]

A transactional email is an automated message triggered by something a specific person did, or something that happened to their account, and it carries information they’re expecting or that they need to complete an action. Receipts. Password resets. Shipping updates. Two-factor codes. The definition is the easy part. The interesting part is the line that […]

The rules quietly changed in February 2024. If your unsubscribe guide is older than that, it’s giving you 2014 advice for 2026 inboxes. Here’s what happened. Gmail and Yahoo started enforcing new requirements for any sender pushing more than 5,000 messages a day to their inboxes. One of those requirements: a working one-click unsubscribe, implemented […]

Most email attachment size guides give you a number and call it done. The problem is that the number on the box isn’t the number that actually sends. Encoding adds weight, recipient servers have their own caps, and a 24 MB file can bounce off a 25 MB limit without ever reaching an inbox. This […]

Transactional SMS is the text your customer gets the second something happens on their account. The shipping label is printed. The login attempt fires. The appointment is 30 minutes out. It’s automated, it’s triggered by an event, and it carries information the recipient actually wants. Marketing? That’s a separate animal with separate rules. This guide […]

SMTP relay is the service that takes an outgoing email from your app, website, or device and hands it off to the recipient’s mail server on your behalf. If you send more than a handful of emails a day, especially the automated ones (password resets, order receipts, alerts, newsletters), you’re almost certainly relying on a […]