Your software
My Mautic version is: 4.15
My PHP version is: 7.4.23
My Database type and version is: 10.5.12-MariaDB-1:10.5.12+maria~bionic
Your problem
My problem is: When adding images to our emails they look fine in the preview option but for some reason when we send ourselves a test message all of the images are missing.
is there any chance remote content in your email client is disabled. If it s that might be the reason.
If its not, try looking into source code of email message and see what is the path to the image, if you paste the link to image to browser, does it open an image?
When you see the path, you might get a clue as to why this is happening.
create really simple email with just one image and see if it works
check server permissions
maybe just for test try to use code mode and display an image like so: <img src="https://mail.conservativeblade.com/themes/conservative-blade/assets/cb-logo.png?v8b92a737">