Indeed, drag and drop to mail from the Skitch client hasn't worked for quite some time. As a workaround, I drag to the desktop and after that I drag from the desktop to mail. Still it was a lot better when it integrated with Mac mail immediately. Also since MacOS Catalina, when I take crosshair screenshot of a window, the screenshot will contain whatever is in the background image, but not the windows that is on the top (visible) layer. I hope that both these issues will be fixed at some point.