It's using the python stdlib logging library. You can add a handler to that logger that sends emails or does anything else. It really depends on how you're running your processes how to setup logging properly but in Pyramid (which uses logging.config.fileConfig) it would be done by adding another section to your ini file to catch the "waitress.queue" logger.
[loggers]
keys = ..., waitress_queue
[handlers]
keys = ..., waitress_queue
[logger_waitress_queue]
handlers = waitress_queue
qualname = waitress.queue
[handler_waitress_queue]
class = handlers.SMTPHandler
formatter = generic