mailgun: enable mangling and syncing with subdomains

[ubiratansoares]

AI disclosure

I used Claude Code to get clarifications about these changes and deep search in the wild info on Mailgun's API rate limits.

---

Towards rust-lang/infra-team#297

We tweak the mangling logic to handle a special subdomain we'll introduce to enable the migration (of lists provisioned by team) from Mailgun to Google Groups.

sync does not support dry-runs for Mailgun in CI, so I had to test these changes manually.

echo "Preparing team static api"
cargo run --quiet static-api build
echo

echo "Dry-run changes against Mailgun"

MAILGUN_API_TOKEN=$(op read <path/to/secret>) \
EMAIL_PRIVATE_KEY=$(op read <path/to/secret>) \
  cargo run --quiet -- sync dry-run --services mailgun --src team-api
echo

A part of the output looks like this, I won't share it full since it'd disclose encrypted emails:

# .
# .
# previous output
#
[INFO  rust_team::sync::mailgun::api] deleting route with ID 5c5b479fa4764a000139448d
[INFO  rust_team::sync::mailgun::api] deleting route with ID 6321fe4584c515511ba78994
[INFO  rust_team::sync::mailgun::api] deleting route with ID 6321fe4565c9ab17d6be343e
[INFO  rust_team::sync::mailgun] creating list ^leah(?:\+.+)?@(?:legacy-lists\.)?rustconf\.com$
[INFO  rust_team::sync::mailgun] creating list ^infra-team(?:\+.+)?@(?:legacy-lists\.)?rust-lang\.org$
[INFO  rust_team::sync::mailgun] creating list ^community(?:\+.+)?@(?:legacy-lists\.)?rust-lang\.org$
[INFO  rust_team::sync::mailgun] creating list ^project-vision-doc-2025(?:\+.+)?@(?:legacy-lists\.)?rust-lang\.org$
#
# more output
# .
# .

This approach will delete and (re)create all 96 lists we currently have, rather than updating them in-place. This should be fine from the rate-limiting perspective for a single deploy (no official numbers, but 300 rpm mentioned on issues like this).

After lots of pain, I think this path worths compared with trying to update existing rules in-place and keeping guardrail checks to ensure consistency between the current and the new state (that was my first attempt).

Happy to get input in case I missed something.

[github-actions]

Dry-run check results

[WARN  rust_team::sync] sync-team is running in dry mode, no changes will be applied.
[INFO  rust_team::sync] synchronizing crates-io
[INFO  rust_team::sync] synchronizing github
[INFO  rust_team::sync] 💻 Repo Diffs:
    📝 Editing repo 'rust-lang/rustup':
      Environments:
        ❌ Delete: copilot

[marcoieni]

let's move this above the for loop so we construct the regex once

[ubiratansoares]

Done!