Need to compare first 3 letters to all cells in the same column

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Thursday July 30, 2015
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July 30, 2015
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Help!
I am trying to see if there are similar email addresses in column 1 rows, and I need to compare it to column two rows to see if the first 3 values match anything else in the same column. I also want to some how view the matching cells as well. Please help :)