Mail apps does not use proxy when displaying content

I’m using the mail apps 1.11.7 on my next cloud server. I have setup a proxy in config.php that is working (weather, notifications … are going through it). Access to internet is, for now, allowed so I’m not blocked yet.
The issue I have is that the mail app is not using the proxy setting for displaying content of the emails. The network flow goes directly to internet and ignore the proxy setting.
I have not seen a parameters in the document to use a proxy for this app even though I think it should use the one configured at the server setting (config.php).

Am I missing something obvious ?

That’s because all this happens locally in the browser from which you are accessing your Nextcloud server. The emails itself do only contain text and file atachements. Everything else like rendering CSS and downloading additional content served from 3rd party sources etc. is handeld by the client. If you want to proxy everything what happens in your browser you would have to make sure that all the traffic from that browser goes through that proxy or maybe use a VPN connection or a Remote Desktop connection back to the network where your Nextcloud server resides.

Actually no. My browser does not run on the server. The client (browser) connect to the web interface (on another host), but the mail app does some requests directly. I guess it’s needed to block the objects in the mail.
I have defined iptables rules that log everything on the server and I can see what goes through squid and what doesn’t. And the web requests for the mail contents are sent by the web server.

Yes you’re right, I made a missconception here, sorry for that. Unfortunately I don’t know why Nextcloud Mail does not respect the proxy settings. If you don’t get any answers here, you could maybe open a an issue on GitHub… GitHub - nextcloud/mail: 💌 Mail app for Nextcloud