Migrate from Mailgun

Mailgun's EU region keeps your mail data in Europe, but the company operating it is still US-owned — which matters if EU data handling is why you chose the EU region in the first place. eusend is EU end-to-end: EU infrastructure, EU company, no US parent. The migration itself is small; the send call gets simpler, since eusend has no per-domain API endpoints.

The code change

Install the SDK with npm install @eusend_dev/sdk. Two structural differences: there's no domain argument — the domain comes from your from address, which must be verified — and no form-data plumbing, since the API is plain JSON. Calls return { data, error } instead of throwing.

import formData from 'form-data'
import Mailgun from 'mailgun.js'

const mg = new Mailgun(formData).client({
  username: 'api',
  key: process.env.MAILGUN_API_KEY,
  url: 'https://api.eu.mailgun.net',
})

await mg.messages.create('mg.acme.com', {
  from: 'Acme <hello@acme.com>',
  to: ['user@example.com'],
  subject: 'Welcome',
  html: '<p>Thanks for signing up.</p>',
})

import { Eusend } from '@eusend_dev/sdk'

const eusend = new Eusend(
  process.env.EUSEND_API_KEY
)

await eusend.emails.send({
  from: 'Acme <hello@acme.com>',
  to: 'user@example.com',
  subject: 'Welcome',
  html: '<p>Thanks for signing up.</p>',
})

Field mapping

If you send over SMTP

Mailgun's per-domain SMTP credentials become one credential: username eusend, your API key as the password. Use port 465 with implicit TLS — eusend does not support STARTTLS on 587.

// Before: smtp.mailgun.org (or smtp.eu.mailgun.org), postmaster@ user
// After — one endpoint, fixed username, API key as password, implicit TLS on 465
const transport = nodemailer.createTransport({
  host: 'smtp.eusend.dev',
  port: 465,
  secure: true,
  auth: { user: 'eusend', pass: process.env.EUSEND_API_KEY },
})

Webhooks

The event model is the same — signed HTTP posts per event — so mostly you're renaming things:

Both providers sign with HMAC-SHA256; only the payload layout differs. Note that Mailgun's temporary_fail has no eusend event — retries on soft failures happen inside the platform, and you hear about the final outcome. The webhook docs show the payload and signing scheme.

What's honestly different

• Attachments work, just as JSON. Mailgun takes attachments as multipart file uploads; eusend takes them inline on the JSON body — base64-encode the bytes into attachments[].content with a filename (and optional content_type / content_id for inline images). Up to 20 files, 10 MB combined per message.
• Bring your suppression list.eusend suppresses hard bounces and complaints automatically going forward, but it can't see your Mailgun history. Export your suppressions and keep those addresses out of your sends.
• Mailing-list campaigns wait. Transactional sending is open today; bulk campaigns open as the platform warms. If you use Mailgun mailing lists for marketing sends, plan that part for later.

Before you flip production

• Verify your sending domain and add its DKIM, SPF, and DMARC records — the Domains page generates them. If you sent from a dedicated subdomain like mg.acme.com, you can keep it or take the move as the moment to switch to a cleaner one.
• Migrate against an eu_test_ API key first — test sends are accepted and tracked but never delivered — then switch to eu_live_.
• Keep Mailgun alive for a week or two after cutover so in-flight events and your suppression export have somewhere to come from.