In the Mail App when you mouse over any hyperlink in the preview screen, the URL for the link gets displayed. This always covers what you're trying to preview. Is there a simple setting (not using the cmd line) to turn it off.
This is one of those "well-intentioned" features some programmer included by default in the Mail app which is actually very annoying. The preview window is for previewing a message and NOT the URLs for hyperlinks in that message. I don't want to preview URLs but rather the message.
MacBook Pro 13", 10.12