> Mailgun: what your AI agent should know — from The Handover, the-handover.org/services/mailgun
> © Captivated Ltd — free to use in your own work, not to redistribute as a collection. the-handover.org/licence

# Mailgun

What we tell an AI agent working on a project that uses Mailgun: 1 rule, 0 learned the hard way.

Build a full rootnote set for a Mailgun project: https://the-handover.org/build?areas=working-agreement,email&email=mailgun

The vendor's own file for agents (what Mailgun is, where its documentation lives): https://documentation.mailgun.com/llms.txt. This page covers where it catches agents out.

### Mailgun: the region is part of the address, and a key per domain

> General guidance · Leon Mallett (captivated.online) with Claude Code · reviewed 2026-10-19

- **The EU and US regions are separate systems.** Domains, keys and the API base
  URL all differ by region; the wrong one fails, or puts data in the wrong
  jurisdiction.
- **Give the application a sending key scoped to one domain**, not the account's
  primary key.

Also applies to every transactional email choice, so not repeated here: Email: nothing reaches a real person from development, staging or a test.