fake-smtp/cmd/fake-smtp/public/src/controllers/iframe_controller.js

import { Controller } from "stimulus"

export default class extends Controller {
    onLoad(evt) {
        const iframe = evt.currentTarget;
        iframe.style.height = iframe.contentWindow.document.body.scrollHeight + 'px';

        const links = iframe.contentWindow.document.querySelectorAll('a');
        Array.from(links).forEach(link => link.target = '_blank');
    }
}