So, if the image you want to put into your email is not hosted somewhere, what’s the best way to go about this, ensuring compatibility?
You can base64-encode the image file. It’s super-jank, but it works, even in Outlook. Example: https://www.base64-image.de/tutorial
Yep, Adobe software still phones home even when it’s cracked. But there’s supposedly a list of hosts you can block to stop this behaviour: https://a.dove.isdumb.one/list.txt