Universal Email cannot be used in Dreamweaver CS5.x, it was not updated to work in CS5.x. Universal Email 4 was released to replace Universal Email 3 before Dreamweaver CS5.x was released.
If you want to use Universal Email 3, you will need to use it in the older version of Dreamweaver
The upgrade to Universal Email 4 is not a free upgrade, it is offered to existing owners of Universal Email at a discounted price, for details please contact our sales department.