An original code (correct rendering):
A email with the code (wrong rendering: extra empty lines are added, the screenshot is taken in the GMail web interface):
Are you sure there are empty lines there and its not simply that the CSS is a bit off?
The line breaks between the
<li> tags are preserved because the code is inside the
Additionally, each line of code has a bottom padding of 10px:
Now it became even worse: the violet background now covers only a part of the code block: