To remove duplicates from your list, you'll paste your list into one column and run a formula to copy addresses without duplicates into a new column.
Open Microsoft Excel.
Paste your entire list into Column A.
Sort the entire column alphabetically, descending (A to Z).
Click the "B" column label to highlight all of Column B.
Highlight Column B in Excel file
With Column B highlighted, input the following formula in the fx field.
With the entire Column B still selected and the formula in the fx field, click Edit in the navigation.
Choose Fill in the drop-down menu, and choose Down. This loads Column B with the addresses from Column A, with duplicates already removed.
To copy this column into a new spreadsheet, click to select Column B.
Click Edit, and choose Copy from the drop-down menu.
Create a new spreadsheet.
In the new spreadsheet, click Edit.
Choose Paste Special from the drop-down menu, and choose "Values."
Further edit or sort this spreadsheet, and save it as your final list. Note that if your list is very large, and you had a lot of duplicates, you may see a number of blank fields at the top of your list. Scroll down to find your email addresses.