latest promo emails from gog.com using increasing amount of cache usage in thunderbird.
in the past one promo email from gog used to use 5-6mb of cache in thunderbird. now opening one email from gog causes cache to grow 30+mb! why? how can i stop that shenanigans and return to normal cache usage when opening emails from gog? are newer gog emails overloaded with huge graphics or some scripts nobody needs? i want this bullshit to stop and return to normal behavior!

Welcome to the new age, where devs often don't give a rats about browser bloat. And yes, emails are often html based, so can suffer the same kind of bloat.

Basically we are talking about image files, that are much bigger than they need to be. A product of lazy developing or a stupid mindset, that thinks everyone has a super duper PC, and if you don't, too bad.

And of course, we are also talking about a ton of scripts also running, most of them totally unnecessary and or poorly written. So bloat all round.

As has been happening over years now, it just keeps getting worse.

It is like AV, where they think it perfectly okay to brute force things due to increased power in modern PCs ... not an obvious issue, maybe, providing of course that your PC has enough grunt.

What they do now, and get away with, would have been seen as worse than most virus a few years ago. In a way, it is a bit like DRM, imposed on everyone due to a few bad eggs and very flawed thinking.

But then, what do you expect with a modern regime that treats most folk like imbeciles.

Step 1: Set your emails to plain-text only, you don't and shouldn't need HTML emails for getting information.

Step 2: Realise GOG emails are HTML only.

Step 3: Unsubscribe!

And cut down on titles on your wishlist ... I'm down to 10, and 6 of those may never come out.

Before you go full plaintext-mode as suggested by lupineshadow, you could try to disallow the loading of "remote content" for html emails. There is a setting for this in Thunderbird's settings' Privacy category, see image attached.

Yes, modern html emails -- especially those advertising "newsletters" -- are crammed full of links to external sources. Upon viewing, these automatically load scripts, ad trackers and images from many sources, not only from the vendor but 3rd-party too. Mind though that this isn't GOG's wrongdoing alone. The newsletters of Steam, Humblebundle and many other web stores aren't any better in that matter.

As already explained by Timboli, email clients need to be treated as web browsers. Another option thus could be to install privacy-oriented extensions. A problem is that at one point the development of Thunderbird split off from that of Firefox, which makes it harder to maintain extensions for both. For example, Ublock Origin only supports older versions of TB up to 52.