I'm a little foggy on when you must, or should, use Certified Mail with return receipt to correspond with a taxpayer.

At present, my understanding is that you must use it when you hold a Certificate and wish to start the 6 month evictment eligibility clock.

However, I deal mostly with deeds and it's not clear that I need to use CM w/RR at all.  Thoughts?

@Arnold Finkelstein , the ONLY time a CMRRR letter is REQUIRED is when you are sending notice letters to lienholders about the tax sale, to run out their one year to redeem (or three years administrative, whichever is longer.)  All other times it is sometimes advisable to send letters by regular and certified mail, but it is not required.

@Denise Evans  I sent the notice to the taxpayer by CMRRR and a week later by regular mail. The CMRRR was returned to me (no authorized recipient available). The second letter didn't come back and I assume it was delivered. Is that enough to start the 6 month clock?

@Thomas Kramer , If you sent the regular mail letter to the correct address, then that is enough to start the 6 month clock ticking down for the notice to vacate letter.  Because it starts upon receipt, you should do everything you can to make sure that is the correct address. You might ask a neighbor. 

@Denise Evans , could the taxpayer not later credibly argue that they never received it, assuming they are savvy enough to do so?

@Arnold Finkelstein , Anybody can lie about anything. If you addressed it to the correct address and sent it by regular and by certified mail, especially if you sent them a week apart, it is HIGHLY unlikely they were both lost in the mail. The law assumes the regular mail one was received three days after it was sent.

@Denise Evans  Thank you for clarifying! I used the most recent mailing address from the tax records (same address on certificate). Of course, if the taxpayer moved and didn't update the address, then he didn't receive the letter.

I also want to thank you for your book! It helped me a lot. :)

@Thomas Kramer google the person, and talk to the neighbors. Somebody knows if he still lives there or not.  Glad the book was a help!