first, check your State's eviction law, every state is different

then follow it to the letter,

second: always use "掛號信", not "普通信".  you can not prove they have received "普通信".  But for "掛號信", the day start counting when post office delivered the letter, regardless whether it is clamed or not.  Again, check the language of your state law.

Third:  If you not sure, better spend a couple of hundread dollars and hire a lawyer.