SendGrid vs Mailchimp Transactional

1. Inventory SendGrid-specific behavior

List every sender, dynamic template, personalization field, attachment, category, scheduled send, suppression rule, and Event Webhook consumer. A successful API response alone does not prove those behaviors survived the migration.

2. Map the send payload

Replace SendGrid's personalizations, from, and content structure with Mailchimp Transactional's message.to, message.from_email, message.subject, and message.html fields.

const mailchimp = require("@mailchimp/mailchimp_transactional")(
  process.env.MAILCHIMP_TRANSACTIONAL_API_KEY
);

await mailchimp.messages.send({
  message: {
    from_email: "receipts@example.com",
    to: [{ email: customer.email, type: "to" }],
    subject: "Your receipt",
    html: receiptHtml,
  },
});

3. Recreate templates and event handling

SendGrid Dynamic Template IDs and webhook payloads are provider-specific. Rebuild each template, translate merge fields, and map Mailchimp Transactional webhook events into your internal delivered, bounced, rejected, complained, and unsubscribed states.

4. Authenticate the domain before traffic moves

Complete Mailchimp Transactional's sender-domain verification and DNS authentication separately. Keep the SendGrid configuration available until the new domain passes your own SPF, DKIM, DMARC, inbox-placement, and reply-path checks.

5. Canary, observe, then cut over

Route a small percentage of eligible messages through the new provider, without sending duplicate customer emails. Compare acceptance, delivery, bounce, complaint, latency, and webhook-processing results. Increase traffic only after those checks pass, and retain a tested rollback path.