your network preferences prevent content from loading privately.

Yes, it does have something to do with it.

With Mail Privacy Protection enabled, it will load remote content (images where the source is from a web site) using two independent relays to anonymize the request so spammers won't know the request came from your IP address.

If the network settings cannot support the double relay, and you have Mail Privacy enabled, it won't load the remote content without pressing the Load Content button. You can disable Mail Privacy Protection in the Settings, Privacy Tab so it will always load the remote content without having to click the button.

Disable all of the checkboxes on the Privacy tab of Mail Settings.