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Are you using mail, or some online email thing such as yahoo or hotmail? If you ask for help, please try to include all relevant information.
 
If you deleted them, they will be in the trash. If you deleted them from there, they will be in:
MacHD/users/<yourusername>/library/mail/<the account name: eg POP-XXXX@gmail.com>/deletedmessages.mbox/messages
I'm not sure how long they last in there, but good luck :)

EDIT: Sorry, left out the bit in bold
 
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