Blog
Practical notes on sending email. The stuff that breaks, the distinctions that matter, and how to let an agent send without regretting it.
- 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
- Troubleshooting
Why DKIM verification fails (and how to fix each cause)
The concrete reasons a DKIM check fails after you've published the key: selector mismatch, a truncated public key, DNS flattening, and message modification in transit.
Unitpost · July 27, 2026
- Deliverability
Why your transactional email goes to spam
A diagnostic order of operations for transactional mail landing in spam: authentication, reputation, content, and the engagement signals you can't see.
Unitpost · July 27, 2026
- AI Agents
What is an email MCP server?
How Model Context Protocol exposes email sending as agent tools, what a well-designed email MCP surface looks like, and how authentication and scopes work.
Unitpost · July 27, 2026
- 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
- AI Agents
How to let an AI agent send email safely
The concrete controls that make agent-initiated email safe: scoped credentials, a verified-domain gate, idempotency, approval before send, and an audit trail.
Unitpost · July 27, 2026
- Troubleshooting
How to fix an SPF record that isn't found
Why an SPF lookup returns nothing even after you've added the record, and how to diagnose it: propagation, wrong host, quoting, and the one-SPF-record rule.
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
Comparisons
How Unitpost compares with other email providers, including where they are the better choice.
- Unitpost vs ResendA developer-first transactional email API, known for the cleanest DX in the category and for React Email.
- Unitpost vs SendGridThe Twilio-owned incumbent, processing billions of emails a month across transactional and marketing with deep enterprise tooling.
- Unitpost vs PostmarkA transactional-only specialist with the strongest deliverability and time-to-inbox reputation in the category.
- Unitpost vs MailgunSinch-owned email infrastructure aimed at developers, with strong validation and deliverability tooling.
- Unitpost vs BrevoAn all-in-one marketing platform (formerly Sendinblue) covering email, SMS, chat, and CRM, with a transactional API alongside.
- Unitpost vs LoopsA modern, design-led email platform aimed at SaaS companies, focused on marketing sequences and lifecycle email.
Send email your users actually receive
5,000 emails a month free — API, SMTP, templates, tracking. No credit card.