Ejectment: Notification of Defendant

[Arnold Finkelstein]

I have a tax deed for a Jefferson County property and am considering ejectment.  When filing, one can choose to have the taxpayer notified via certified mail with return receipt.  

Must that return receipt be received by the sheriff in order for the case to go forward, or does their simply sending it mean the case can move forward?  What if the taxpayer no longer lives at the address they gave the county when they recorded/assessed their property, and they never get the certified mail?

As the plaintiff is asked to provide the court clerk the address for the taxpayer/defendant, the one the court uses to notify them, what are the plaintiff's responsibilities here?  How do we really know where the taxpayer lives?  What if we're wrong?