---
title: "Blog"
description: "Email engineering guides for developers and agents."
url: https://www.unitpost.com/blog
section: "Blog"
updated: 2026-07-31
---

# Blog

> Email engineering guides for developers and agents.

HTML hub: https://www.unitpost.com/blog

- [How to fix an SPF record that isn't found](https://www.unitpost.com/blog/spf-record-not-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. ([Markdown](https://www.unitpost.com/blog/spf-record-not-found.md))
- [Why DKIM verification fails (and how to fix each cause)](https://www.unitpost.com/blog/dkim-verification-failing): 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. ([Markdown](https://www.unitpost.com/blog/dkim-verification-failing.md))
- [Why your transactional email goes to spam](https://www.unitpost.com/blog/email-going-to-spam): A diagnostic order of operations for transactional mail landing in spam: authentication, reputation, content, and the engagement signals you can't see. ([Markdown](https://www.unitpost.com/blog/email-going-to-spam.md))
- [Transactional vs marketing email: what's the difference?](https://www.unitpost.com/blog/transactional-vs-marketing-email): The practical distinction between transactional and marketing email — consent, unsubscribe obligations, reputation risk — and when one tool for both is the right call. ([Markdown](https://www.unitpost.com/blog/transactional-vs-marketing-email.md))
- [What is an idempotency key, and when do you need one?](https://www.unitpost.com/blog/what-is-an-idempotency-key): How idempotency keys prevent duplicate sends when a request is retried, how to choose one, and the failure modes they don't cover. ([Markdown](https://www.unitpost.com/blog/what-is-an-idempotency-key.md))
- [Why domain verification should never be a one-time check](https://www.unitpost.com/blog/continuous-domain-verification): 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. ([Markdown](https://www.unitpost.com/blog/continuous-domain-verification.md))
- [How to let an AI agent send email safely](https://www.unitpost.com/blog/send-email-from-ai-agent): The concrete controls that make agent-initiated email safe: scoped credentials, a verified-domain gate, idempotency, approval before send, and an audit trail. ([Markdown](https://www.unitpost.com/blog/send-email-from-ai-agent.md))
- [What is an email MCP server?](https://www.unitpost.com/blog/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. ([Markdown](https://www.unitpost.com/blog/email-mcp-server.md))