The correct way of addressing a Catholic priest is The Reverend John Smith, J.C.D. (the initials for his doctorate are OPTIONAL) on the envelope. The head of the letter would be Dear Father or Dear Father Smith, and in conversation, Father or Father Smith (if there are more than one around). You do not normally acknowledge a priest's degrees in addressing him, unless there is a reason, like in a footnote, then The Reverend John Smith, J.C.D.
Assuming that you're sending the card to a male who has been both ordained by an organized religious body and earned a doctorate in any field of study but usually in this case, a Doctor of Divinity (DD), "Reverend Doctor _" (Rev. Dr. _) is exactly correct.
doctorate degree
The former is the usual form: I have a doctorate.
Formally it would be "The Reverend John Smith" - but only in the third person. Note that the definite article is required, as are both first name and surname. If you are using the second person, for example when addressing him in speech or writing, the correct form of address is "Mr Smith".
Reverend Herman Sampson, Pastor
It is correct when addressing an animal with that name.
The correct spelling is "reverend" (a clergyman).
Both are correct. My question is it no longer correct to address him as "Reverend"? This is what he signed his writings with and it is also on his tombstone but it seems he is no longer called this.
The Reverend (first name) and Mrs. (first name) SurnameNote that the title "The Reverend" takes the first name not the surname. Thus, if John Smith is ordained his correct title is not "The Reverend Smith" but "The Reverend John Smith". Note also that a definite article is required: "The Reverend", never simply "Reverend".Just Reverend is for conversation only when speaking to the Reverend face to face.
Dear Father, Dear Reverend Father or Most Reverend Father
No - Transport layer protocols are not concerned with addressing packets to the correct system. (True)
On the envelope: The Reverend Father (full name) or The Reverend (full name). In the letter, address him as "Dear Reverend Father (name) or Dear Father (name ). In person, the correct greeting is, "Hi, Father (first or last name as he prefers)" or "Hi, Reverend Father (first or last name as he prefers). Using the priest's first name, "Hi, Father Joe!", is not technically proper but many priests prefer it. One should ask the priest what he prefers.