A simple batch campaign can solve quickly.
Smart list : Email is empty
Flow : Delete Lead
The best tool for the job is a Smart List in my opinion. Create a new Smart List in Lead Database (and call it something like No Email Address) then in the filter section, drag in Email Address and select in the dropdown "is empty".
You'll then have a Smart List made up of leads which you can choose to delete (using Delete Lead at the top) or any other action you wish to take on this list.
Does that answer your question, Lucy?
EDIT: Breno's solution is even quicker, skipping the list creation step. You can easily automate the process from there too, by scheduling it to run every day, for example!