Author: Saul

A DKIM selector is the label in a DKIM-Signature header’s s= tag that points a verifier to the right public key in DNS. Here’s how to find yours, read a real DNS lookup, and rotate selectors without breaking signatures still in transit.

How email OTP works: code length, expiry, hashed storage, and rate limits, plus how it compares to magic links and SMS OTP for login verification.

A magic link email authenticates a user with a single-use, expiring token instead of a password: click the link, land in an authenticated session. This covers the token contract, the security risks unique to email-based auth, and how magic links compare to email OTP and passwords.

A catalog of the 11 transactional email types every SaaS product sends, from welcome and password reset to receipts, invoices, and dunning notices, with what to include and a short example for each.

An invoice email needs the invoice number, due date, and total due in the body itself, not just the attached PDF, plus a working payment link and a sender address someone monitors. This guide covers what to include, subject line and reminder timing, deliverability, and a copy-paste template.

Dark mode doesn’t mean one thing across email clients. Apple Mail leaves your HTML untouched, Outlook.com flips only pure black and white, and Gmail’s iOS app rewrites colors throughout the message. Here’s how to control all three with CSS and keep logos legible everywhere.

A dedicated sending IP has no history, so mailbox providers judge it purely on what you do in the first few weeks. Learn the mechanics, a representative warmup schedule, and how to monitor progress on a dedicated IP.

A breakdown of Brevo’s pricing tiers, email-volume limits, and the contact-based vs. volume-based billing distinction, verified against the official pricing page as of July 2026.

A noreply@ sending address blocks replies, invites spam complaints, and gives up the engagement signals mailbox providers reward. Here is what the data says, the narrow cases where it still holds up, and what to use instead.

A breakdown of Mailgun’s Free, Basic, Foundation, and Scale plans, overage rates, dedicated IP and validation add-ons, and Mailgun Optimize’s separate pricing, verified against the official pricing page as of July 2026.

Twilio SendGrid actually sells two separate products with two separate price lists: Email API (transactional and programmatic sending) and Marketing Campaigns (contact-based email marketing). As of July 2026, Email API runs from a free 100 emails/day tier up through Essentials ($19.95/mo for 50,000 emails), Pro ($89.95/mo for 100,000 emails), and custom-priced Premier. Marketing Campaigns bills…

A breakdown of Resend’s pricing tiers, free tier limits, overage rates, and a worked cost example, verified against the official pricing page as of July 2026.