routes_onerror = [
    ('myapp/*', '/myapp/default/handle_error')
]

Controller ({app}/controllers/default.py):

def handle_error():
	""" Custom error handler that returns correct status codes."""
	
	code = request.vars.code
	request_url = request.vars.request_url
	ticket = request.vars.ticket

	if code is not None and request_url != request.url:	# Make sure error url is not current url to avoid infinite loop.
		response.status = int(code) # Assign the error status code to the current response. (Must be integer to work.)

	if code == '403':
		return "Not authorized"
	elif code == '404':
		return "Not found"
	elif code == '500':
		
		# Get ticket URL:
		ticket_url = "<a href='%(scheme)s://%(host)s/admin/default/ticket/%(ticket)s' target='_blank'>%(ticket)s</a>" % {'scheme':'https','host':request.env.http_host,'ticket':ticket}

		# Email a notice, etc:
		mail.send(to=['admins@myapp.com '],
					subject="New Error",
					message="Error Ticket:  %s" % ticket_url)
		
		return "Server error"
	
	else:
		return "Other error"