Q:

Magento 2 - How to add custom block/template to transactional mail?

In order confirmation email I want to add custom block/template (phtml file). How can I achieve it?

A:

We can do like this:
{{block class='Magento\\Framework\\View\\Element\\Template' area='frontend' template='Vendor_Module::email/custom.phtml'}}

See more here: vendor/magento/module-sales/view/frontend/email/shipment_new.html

