Duplicate emails in two columns

Hello,

I have two rows of approximately 2000 email addresses, One from our Accounts package database, another from our website database. Can anyone tell me how to run a search to highlight any duplicate email addresses from either of by rows? Example below

Customer (a) Accounts email (B) Website email (C)
toys rus info@toysrus.com sales@tesko.com ****dup
tesko sales@tesko.com sales@menco.com
liddles info@liddles.com email@harvestor.com
aldy sales@aldy.com sales@aldy.com ****dup


for instance the search needs to highlight tesko & aldy email address, the email addresses are obvoulsly not on the same line as each other so do not match up easily

Please can someone help

Thanks