mailgun-setup

name	mailgun-setup
description	Set up and send emails via a user-provided Mailgun account (BYO email provider)
compatibility	Designed for Vellum personal assistants
metadata	{"icon":"assets/icon.svg","emoji":"📬","vellum":{"category":"email","display-name":"Mailgun Email Setup","user-invocable":true}}

Overview

Send emails through the user's own Mailgun account. The user provides their Mailgun API key and domain, and you send via their infrastructure.

Setup

Step 0: Check Existing Configuration

Before starting, check whether Mailgun is already configured:

bun skills/mailgun-setup/scripts/check-config.ts

The script outputs JSON: { "configured": boolean, "hasApiKey": boolean, "hasWebhookKey": boolean, "details": string }.

• If configured is true — Mailgun is already set up. Offer to verify the connection or reconfigure.
• If configured is false — continue to Step 1.

Step 1: Store the API Key

Run the store script to securely collect the API key:

bun skills/mailgun-setup/scripts/store-api-key.ts

The script opens a secure credential prompt, stores the key, and exits. If it exits 0, the key is stored. Exit code 130 means the user cancelled the prompt — nothing was stored; that's a valid choice, not an error, so ask whether they'd like to try again rather than treating it as a failure. Any other non-zero exit is a real failure. Never ask for the key in chat.

Note: Mailgun uses HTTP Basic Auth with username api and the API key as the password. The credential proxy cannot construct Basic Auth headers automatically. Instead, use curl -u "api:$KEY" in bash commands — retrieve the key from the vault at runtime. See the sending examples below.

Step 2: Detect the Domain

After storing the API key, automatically detect the user's domain — don't ask them for it. Retrieve the API key from the vault and call the Mailgun Domains API:

curl -s --user "api:$MAILGUN_API_KEY" \
  https://api.mailgun.net/v4/domains?state=active

The response contains an items array of domain objects with name and state fields. Pick the first domain with "state": "active". If no active domains are found, try the EU endpoint (https://api.eu.mailgun.net/v4/domains?state=active). If still none, tell the user they need to verify a domain in their Mailgun dashboard first.

Use hi@<domain> as the default sender address. Remember the domain and region (US/EU) for future sends.

Step 3: Verify the Connection

Confirm the API key works by checking the domain response returned in Step 2. A successful response (HTTP 200) with domain data confirms the connection.

Step 4: Webhook Setup (for receiving email)

If the user also wants to receive emails via Mailgun, run the webhook setup script:

bun skills/mailgun-setup/scripts/setup-webhook.ts --domain "<verified domain>" [--region eu]

This script:

1. Registers a callback URL via the webhooks system
2. Creates an inbound route in Mailgun via their API
3. Prompts the user for their webhook signing key (found in the Mailgun dashboard: Settings > API Security > HTTP Webhook Signing Key)

If the script fails because no public base URL is configured (self-hosted only), load the public-ingress skill to walk the user through setting one up, then retry.

Step 5: Report Success

Summarize with the completed checklist:

"Setup complete! ✅ API key configured ✅ Domain detected: <domain> (region: US/EU) ✅ Connection verified {webhook_line}

Default sender: hi@<domain>"

For {webhook_line}:

• If webhook was set up: ✅ Inbound route and webhook signing key configured
• If skipped: ⬜ Webhook — run setup again to enable inbound email

Sending Email

Use bash with curl to call the Mailgun API. Pass the API key via -u for Basic Auth:

curl -s --user "api:$MAILGUN_API_KEY" \
  https://api.mailgun.net/v3/DOMAIN/messages \
  -F from="Name <[e-mail]>" \
  -F to="[e-mail]" \
  -F subject="Hello" \
  -F text="Plain text body" \
  -F html="<p>HTML body</p>"

Replace DOMAIN with the user's Mailgun sending domain.

API Parameters

Parameter	Type	Required	Description
from	string	✅	Sender address ("Name <email>" format)
to	string	✅	Recipient(s), comma-separated for multiple
subject	string	✅	Email subject
text	string		Plain text body
html	string		HTML body
cc	string		CC recipients, comma-separated
bcc	string		BCC recipients, comma-separated
h:Reply-To	string		Reply-to address
h:In-Reply-To	string		Message-ID of parent (for threading)
h:References	string		Space-separated chain of ancestor Message-IDs

Threading (replies)

To reply in a thread, include custom headers:

curl -s --user "api:$MAILGUN_API_KEY" \
  https://api.mailgun.net/v3/DOMAIN/messages \
  -F from="[e-mail]" \
  -F to="[e-mail]" \
  -F subject="Re: Original subject" \
  -F text="Reply body" \
  -F "h:In-Reply-To=<original-message-id>" \
  -F "h:References=<original-message-id>"

Response

Success returns { "id": "<message-id>", "message": "Queued. Thank you." } with HTTP 200.

Errors return { "message": "error description" } with 4xx/5xx status.

Regions

Mailgun has US and EU regions:

• US (default): https://api.mailgun.net/v3/DOMAIN/messages
• EU: https://api.eu.mailgun.net/v3/DOMAIN/messages

Ask the user which region their account uses if sends fail with 401.

Important Notes

• The from address must be from the user's verified Mailgun domain.
• Default sender address is hi@<domain> — use this unless the user specifies otherwise.
• Always confirm with the user before sending — never send without explicit permission.
• Use text for plain text, html for rich formatting. Provide both when possible.
• Mailgun's free tier allows 100 emails/day. Paid plans have higher limits.