Flask blueprints with gevent working outside of application context
For historical purposes: putting the from myproject.app import create_app inside the send_async_email instead of at the top of with the rest of the imports solved the ImportError, because it caused a circular dependency.
You need to define your async function within your view and use the @copy_current_request_context decorator, so that it can have access to the current request (and app) context.
For details: documentation of flask.copy_current_request_context.