Shopify’s contact form posts to Shopify unless the theme says otherwise.

What the theme actually contains

A Shopify contact page is a Liquid section. Somewhere in it is a {% form 'contact' %} tag, which is what routes submissions to Shopify. Replacing that with a plain HTML <form> pointing at the endpoint is the whole change, and it belongs in a custom section so a theme update cannot undo it.

{% schema %}
{
  "name": "Contact form",
  "settings": [
    { "type": "text", "id": "endpoint", "label": "Form endpoint" }
  ]
}
{% endschema %}

<form action="{{ section.settings.endpoint }}" method="POST">
  <label for="shopify-email">Email</label>
  <input id="shopify-email" name="email" type="email" required>

  <label for="shopify-message">Message</label>
  <textarea id="shopify-message" name="message" rows="5" required></textarea>

  <button type="submit">Send</button>
</form>

The endpoint is a setting rather than a literal, so the same section works on a staging theme pointing at a test form and a live theme pointing at the real one.

Three transitions to plan

• Notifications. Shopify stops sending; verify the endpoint’s recipients before switching.
• Success state. Shopify showed its own confirmation. Set a redirect or accept the endpoint’s page.
• Old submissions. Anything already in Shopify stays there. Export it if it matters, because the two lists will never merge.

Why this is often the right move on Shopify

Shopify handles orders well and support-style forms adequately. The moment a form needs routing, a file upload, a webhook into another system, or a record that a non-Shopify tool can read, the endpoint does the job without touching the storefront or the checkout.