The question included the fact that the images are embedded in the normal way using IMG SRC = filename, where filename is in the form D:\folder\image.png

Read the release notes. https://www.mozilla.org/en-US/thunderbird/52.0/releasenotes/

Propellerhead said

HTML signature file containing 2 images using the correct HTML . Worked fine until Thunderbird Ver 52.0.1, which now blocks the image content until manually unblocked for every email sent.

Sorry, I did not make myself clear. I understand the general principle of blocking images in ver 52. However, this is a very annoying thing if it means having to unblock the images in my signature every time I send an email.

I set the config mail.compose.attach_http_images from false to true, which I understood would fix this problem, but this has made no difference - every signature still requires 2 unblocking actions for the same old images used each time.

The signature html file was composed and edited using an external text editor, so I don't see how to get round this problem.

Surely there is a way to make these images trusted somehow?

Open a new 'Write' window and remove all content and signature, so it is completely empty. Please recreate the signature using an image that is stored on your computer and save as a html file. Then,in Account Settings set that new signature html file as the one to use.

Also, note the DATA Url has changed for images and it might be causing the issue.

Basically, use 'Write' to create the signture html file.

Thank you Toad-Hall.

OK, now I see the difference. The IMG specifications now embed the images in the html file rather than reference a separate file on disk. This is how I updated my signature file - quite simple, really:

• Create new html signature file with a different filename, as explained above, listing all image files (no text necessary).

• Edit original signature file, replacing the original IMG SRC statements for each image with the new IMG SRC statements for the same images and save.

The updated html file is identical to the old, the blocking issue resolved.

Unfortunately, with my very limited knowledge of html, the answer doesn't help.

When I created my signature originally, I followed the article found at URL https://support.mozilla.org/en-US/kb/signatures - which I guess is now out of date.

I could do with "for Dummies" advice on how to implement the new requirements.