Conditional formatting is the quickest and easiest way to find duplicates on a single sheet. We’re going to use this technique to sort through this database of email addresses, weeding out any duplicates that have arisen thanks to users submitting the same information more than once, and registering the same address under more than one name.
The first step is to select all the data we want to scour for duplicates. Then, head to the Styles section of the Home tab and navigate to Conditional Formatting > Highlight Cells Rules > Duplicate Values.
This will bring up a window that allows you to customize the way that duplicate values are styled. This is an optional step, so if you’re just looking to find duplicates and don’t care about the color scheme, click OK to move on.
You should find that any duplicate entries are now highlighted in red. This should make it easy for you to delete unnecessary cells, or even at least understand at-a-glance which information is extraneous.