Render HTML message in iFrame

[jenlampton]

Problem/Motivation
HTML based emails are displayed with the raw html code. I would like to render these emails when viewing the mail log.

Steps to reproduce
send an html email with logging enabled and view it from Maillog

Proposed resolution
Detect when and email is HTML and render it in an iFrame

Remaining tasks
implement this new feature.

User interface changes
add an option to enable this feature.

This is a copy of the drupal issue from https://www.drupal.org/project/maillog/issues/3225133. It looks like there's a MR there that's failing tests.

[laryn]

I'm open to this, sounds good.

[laryn]

Looks like there hasn't been any additional work over there, but it looks like the top four commits here are the changes proprosed (which would need slight adjustment for Backdrop):

• https://git.drupalcode.org/issue/maillog-3225133/-/commits/3225133-render-html-message