use google-app-engine firewall to receive email relay from specific IP

Question

we have a GAE email receiver, which is able to receive email from specific IP, now our we want to emails from this IP only , and reject others ip. we use GAE-firewall to set deny all but only allow this ip, but it does not work. I set deny all ip as default(the default rule),then set allow rule for specific IP with priority, I could use browser to access this app-engine instance, but firewall rejects all coming emails, include the my laptop which I can access this app-engine instance by browser, how should I config that to achieve receive email from specific IP only? the seting is: priority for specific ip is "1", priority for deny all is "default",sorry for the image not shown