User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:76.0) Gecko/20100101 Firefox/76.0

Steps to reproduce:

Opened an email. Where it said "To protect your privacy, Thunderbird has blocked remote content in this image", from Preferences drop down I selected "Show remote content in this message".

Actual results:

Image did not display, just got the "broken image" icon.

Expected results:

The image should have displayed. Earlier versions of Thunderbird (I can't remember how far back) did display the image, because I starred a message from April 14, 2020 that had an image that I distinctly recall seeing, and today it wouldn't display. (On April 14, I was using either 68.6.0 or 68.7.0).

A command-U shows this as the image URL in the email body:
<p><img alt=3D"" src=3D"https://www.betham.org/_preview/large/uploads/Torah=
-Study/TorahStudyBlessingandKaddishdRabbanan.jpg" style=3D"width: 800px; he=
ight: 1035px;"></p>

I suspect that the HTML processor is not properly processing the "=<NL>" sequence, and maybe not even the "=3D" sequence, because if I manually construct the URL to this:
https://www.betham.org/_preview/large/uploads/Torah-Study/TorahStudyBlessingandKaddishdRabbanan.jpg
and paste it into Firefox, it displays.

This is just one example.

Forgot to say today I'm using Thunderbird 68.8.0.

I opened the Error Console, cleared it, selected all options (I've never used it before), and reloaded the message. I uploaded the error console. Here is a (reconstructed) portion:
Request URL: https://www.betham.org/_preview/large/uploads/Torah-Study/TorahStudyBlessingandKaddishdRabbanan.jpg
Request method: GET
Remote address: 23.217.138.110:80
Status code: 404 Not Found (?)
Version: HTTP/1.1

But 23.217.138.110 is not the IP address of www.betham.org. Using Lookup in Network Utility, I get:
23.217.138.110 -> a23-217-138-110.deploy.static.akamaitechnologies.com
and
www.betham.org -> 52.22.170.20, 52.20.111.107, 52.200.239.178

So why is Thunderbird not looking up the address properly? (Note: I've gone off and on a VPN while Thunderbird is up. I find taking Thunderbird offline while switching VPN states, then going back online, helps with its ability to store Drafts and Sent messages.)

I'm going to try Quitting Thunderbird and restarting it and see what happens.

I restarted Thunderbird, and now it is getting the images from the proper IP address:
Request URL: https://www.betham.org/_preview/large/uploads/Torah-Study/TorahStudyBlessingandKaddishdRabbanan.jpg
Request method: GET
Remote address: 52.22.170.20:443
Status code: 301 Moved Permanently (?)
Version: HTTP/1.1

But having to restart Thunderbird when I switch VPN states is just a workaround; Thunderbird should handle that better. (Firefox seems to have no problem with it.)

I don't know if this is related, but toggling online/offline only works for Sents. If I try to Save As->Draft a message I'm writing after I've gone off of VPN, even if I start writing the message after I've first gone off of VPN and toggled offline/online and done a Get Messages, it stays in the "Copying message to Drafts folder..." state forever (until I Cancel it, of course).

(In reply to Steve Chessin from comment #6)

I don't know if this is related, but toggling online/offline only works for Sents. If I try to Save As->Draft a message I'm writing after I've gone off of VPN, even if I start writing the message after I've first gone off of VPN and toggled offline/online and done a Get Messages, it stays in the "Copying message to Drafts folder..." state forever (until I Cancel it, of course).

I should have said that this is for a message using my employer's IMAP/SMTP server, and it resolves to a different IP address when on the VPN than when off it.

I don't know that it will be any better, but are you able to test version 78?

I've been working from home since the pandemic, with a different configuration (work computer always on VPN, personal computer never on VPN), so I haven't attempted to reproduce the problem.

Steve,
Passible to test now?

I'm afraid not. Still working from home. Maybe in a month or two.

Steve, Able to test now?

Hi Wayne. I'm afraid not. Working from home has turned out to be more convenient than working from the office, so unless and until my employer demands that I work from the office, I won't be able to test the change.