Concepts
The distinctions that change how you build.
- Concepts
How email webhooks work (they're POST)
An email webhook is an HTTP POST to your URL when a message is delivered, bounced, opened, or clicked — not polling, not IMAP.
Unitpost · August 27, 2026
- Concepts
Move off SendGrid SMTP after the free plan ended
SendGrid retired its free plan. Point the same SMTP client at Unitpost — host, username unitpost, API key as password — without rewriting your app.
Unitpost · August 27, 2026
- Concepts
Why domain verification should never be a one-time check
DNS changes after you verify a domain. How continuous re-verification with a grace period catches regressions without turning a transient blip into an outage.
Unitpost · July 27, 2026
- Concepts
Transactional vs marketing email: what's the difference?
The practical distinction between transactional and marketing email — consent, unsubscribe obligations, reputation risk — and when one tool for both is the right call.
Unitpost · July 27, 2026
- Concepts
What is an idempotency key, and when do you need one?
How idempotency keys prevent duplicate sends when a request is retried, how to choose one, and the failure modes they don't cover.
Unitpost · July 27, 2026
Send email your users actually receive
5,000 emails a month free — API, SMTP, templates, tracking. No credit card.