Required Excel freelancer for excel formula to highlight duplicates job

I have a large excel file (70,000) with email addresses. I have 1000 or so bad emails. I want a formula that will help me remove the bad emails.

Currently I have a formula that involves putting the bad emails at the end of the email column, sorting them all in alphabetical order so that the duplicates are together and then making an empty column and using the formula to put an x in the new column beside the duplicate.

this is so time consuming


I want a formula that will just identify the duplicates and put an x in the new column without me having to sort them all in order first

Skills & Expertise Required

Excel