You can add another column to the usuarios table called confirm that is boolean. When an user registers this will be set to false. After the insert you can call the mail function.
http://framework.zend.com/manual/1.12/en/zend.mail.introduction.html
You can go in the database and confirm users as you get emails then by switching confirm to true. On your login page you check if the user has been confirm or not by checking that column.
Here is what I could find on the login form. http://framework.zend.com/manual/1.12/en/learning.multiuser.authentication.html
After this line. You would check if the user was confirm or not. if ($result->isValid()) {