Wow... that didn't display nicely. I'll try pasting again here: _____________________________________________________________

Guys... any hints appreciated with this problem, which occupied me without success for many hours last night.

For some time, a particular instance of Thunderbird has not output remote content for one particular domain. And that sounds really basic and easy to solve, except that I've not managed it.

Problem characteristics

• I delete every reference to this domain: in address books, and in Settings>Account>Privacy>Exceptions.
• I'm now shown the 'Show remote content' banner; but if I select to show (by any of the options offered), it still doesn't.
• I can see remote content from other domains on this Thunderbird client
• I can see remote content from the same domain on other Thunderbird clients on another PC on the same network (but not on a copy of Thunderbird Portable I installed to make a test on the same PC)
• I can see remote content if I take the URL from 'View Source'. un-escape it and paste into a web-browser.
• I can see remote content if I forward the e-mail to (for example) gmail on the same PC.
• I can see remote content if I view in a webmail client on the same PC.
• I can see remote content in a different mail client (MailBird) on the same PC.
• Checking a sample tag syntax, it's exactly the same as in other e-mails that do work.
• View Message Body is set to Original HTML
• It's the same whether Settings>Account>Privacy> Allow Remote Content is checked or not
• Both settings of mailnews.message_display.disable_remote_image produce the same result.
• It's the same if I start Thunderbird in Safe Mode, without plug-ins.
• It's the same whether the e-mail originated in a server app, or a webmail app, MS Outlook, or wherever I've received from.

I'm really out of ideas now. Thanks for any help.

What domain? I wonder if your anti virus recognizes the image domain as a source of tracking and blocks it.

Thanks for the idea Matt. I've just had a try turning off Windows Defender and re-checking (that's the only antivirus I have), but still the images didn't show.

It's just my company's domain. (I'll try not to name it here, to avoid it coming-up in search results in this context... if it will help, I'll find a way.) But I've just fed its domain and IP address into a blacklist checker, and it's clear on all (excepting the services that time-out).

Also, the images display in Mailbird client on the same PC. That's a curious thing. I'm not sure whether that completely rules out a PC-related reason. I wonder if there's some way of detecting whether Thunderbird is requesting the images which aren't being delivered; or isn't making the requests.