$htmlLayout public property
HTML layout view name. This is the layout used to render HTML mail body. The property can take the following values: a relative view name: a view file relative to $viewPath, e.g., 'layouts/html'. a path alias: an absolute view file path specified as a path alias, e.g., '@app/mail/html'. a boolean false: the layout is disabled.
public string|boolean $htmlLayout = 'layouts/html'