Excel Macro: Highlight Email Duplicates

I have a contacts worksheet in Excel for Mac that often contains more than one row with the same email address. What I need is a lightweight macro I can trigger from a button or shortcut that will:

• scan the sheet,
• find every email that appears more than once, and
• highlight each duplicated entry in red—nothing is to be deleted automatically.

The highlight-only approach lets me decide, on a case-by-case basis, which full contact row to keep and which to remove. Aside from the red fill on duplicates, the script must leave every other part of the workbook untouched.

Please deliver a ready-to-use VBA module (or an entire macro-enabled workbook if you prefer) that works smoothly in current Excel for Mac, along with a short set of installation and usage notes so I can drop it into future files just as easily.