You can exclude people from receiving the same email by including this statement in a Smart List:
Was Sent Email IS "X"
Then in the Campaign, say
Member of Smart List NOT IN "Was Sent Email IS X" to exclude anyone who received the email.
OR
NOT Was Sent Email IS "X" will return everyone who never received that email.
btw: Was Sent Email IS NOT "X" will return everyone who received any email BUT "X"