Email format validation

 Create a validation rule on any Email_Address Field.

AND(
NOT(ISBLANK( Email_Address__c )),
NOT(REGEX( Email_Address__c ,'^[a-zA-Z0-9._|\\\\%#~`=?&/$^*!}{+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,4}$')))