Hi sr508
As far as i know Campaign cannot validate if a email address is valid or not however there are few websites which i think can.
Now in order to check if an email has been sent or not to a particular recipient, you can open the delivery and click on delivery tab and there you can see if the email has been successful or not. If an invalid user is targeted then then status for that user will be failed and reason column will show the text. For example mailbox does not exist, invalid user, etc..
Regards,
Ananya Kuthiala