The thing with Sonoff (using their eWeLink network) is that they use their own central server (in China), which is a route you (most probably) don't want to take; you can however subscribe your ESP8266 to a MQTT server instead.
See the Tasmota project for more information and ideas.
Another option is to make your ESP into a server and forward it's port inside your router to the outside.
Please note that forwarding any webserver might/will introduce a security issue.