Passing variables from hook_mail to cutom twig template
Rather than using node get to print a value just use this in twig.


  node.field_myfield_name.value


Otherwise preprocess your twig and get only required fields over sending complete node object to twig.

function theme_name_preprocess_mail_body_content(&amp;$variables) {
  $variables['myfield_name'] = $variables['node']-&gt;field_myfield_name-&gt;value; //$variables['node'] will be render $node from your hook_mail() function.
}


And in Twig myfield_name will work