How to compare two columns to find unmatched records in MySQL

Question

I have a MySQL table with 2 columns and each column has thousands of records

For Example 15000 Email addresses in Column1 and 15005 Email addresses in column 2

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Answer 1

Not sure if I got it right... but would it be something like?

select column2 from table
where column2 not in (select column1 from table)