Hi,

I installed Mattermost on a Centos 7 server. The server is only accessible within the LAN, but the server itself does have access to the internet - meaning, ports 80 and 443.

The weird thing is that, after I installed its mobile application for iphone, and being connected to the mobile phone (so from outside the LAN), I could receive notifications of the messages I got from users. At the same time, obviously, I couldn't connect to the server itself - there's no DNAT, port forwarding or anything like that.

So my question is, how was I able to receive these notifications exactly? Of course, it's because the server does have access the internet, but should this be enough? How does it know where to send it, if the mobile's IP is, of course, different from the private one the mobile used in order to configure the application and connect to the server?

It seems that the application is using a default proxy server to push mobile notifications. That's how it was working.