etc/email_templates.xml
<?xml version="1.0" encoding="UTF-8"?>
<!--
/**
* email_templates
*
* @copyright Copyright © 2017 Staempfli AG. All rights reserved.
* @author juan.alonso@gmail.com
*/
-->
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Email:etc/email_templates.xsd">
<template id="staempfli_mailcatcher_email_test_template" label="MailCatcher Test" file="test.html" type="text" module="Staempfli_MailCatcher" area="adminhtml"/>
</config>