Remote Content in Thunderbird - Protected/Proxy Loading?

[Adonnen]

As I understand it, Thunderbird does not load many images in emails by default because the external provider of that image would receive the user's IP address.

It seems like some clients, such as outlook.com and gmail.com, just proxy the remote content so the user's IP is only exposed to the proxy provider (Microsoft and Google).

While Thunderbird is free and open, is there a technical reason this would not work? As I see it, there are two non-exclusive options.

1. Proxy through a third party
I pay for a VPN service, and would appreciate the ability for Thunderbird to use it when retrieving remote content. Would this be possible with an extension?

2. Proxy through Mozilla
Mozilla/Thunderbird uses its own servers to retrieve remote content when enabled in settings.
I would imagine something like:

Settings -> Privacy & Security -> Privacy -> Mail Content -> Retrieve remote content through Mozilla

(Though the settings entry would also be a more elegant solution for third-party services, if possible. Maybe by selecting a system network interface?)