Services
Mailgun
What we tell an AI agent working on a project that uses Mailgun —1 rule.
Build a rootnote set for a Mailgun projectPlain text
Mailgun publishes its own file for agents — documentation.mailgun.com/llms.txt. That is what the tool is and where its documentation lives. This page is the other half: where it catches agents out. Why both.
Everything here is general guidance: rules an agent knows but does not reliably follow. We have not been caught out by Mailgun ourselves, and this page does not pretend otherwise.
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 it is not repeated here:
- Email: nothing reaches a real person from development, staging or a test
All of it is included when you build a set.