What is the appropriate way to address a Hindu priest? When you are speaking to them, and then when you are?

...and also when you are addressing them in a letter? Please don't ask why I don't know this, but I don't and very embarred by that. Is it "Shri", should you find out their name and use it as well? Does it change depending on if they are a priest of Shiva, Mataji, or Vishnu? Thank ou for answering this.