The email delivery system will still attempt to deliver email messages to the email address, regardless of whether or not it is incorrect. If the provided email address does not exist, then a message will not be delivered. However, if the incorrect email address does exist, the email will be delivered to the wrong person.
That is why it is very important that people have properly specified the Alert Email field on their user profile in order for them to receive notifications as expected. Please let us know if you would like further clarification or there is anything else we can do to assist you.