Ambassador - Bishop

Ambassadors
ENVELOPE: "His Excellency Mr. ...."
OPEN: "Dear Mr..."
CLOSE: "Yours sincerely"

Barons
ENVELOPE: "The Right Hon the Lord......" or socially "The Lord...."
OPEN: "My Lord" or socially , "Dear Lord"
CLOSE: "Yours faithfully" or "Yours truly"

Baron's Daughter
ENVELOPE: "The Hon Mrs ....." if married; The Hon [Sarah] .." if unmarried.
OPEN: "Madam"
CLOSE: "Yours faithfully"

Baron's Son
ENVELOPE: "The Hon [Edward] ....."
OPEN: "Sir." or socially "Dear Mr....."
CLOSE: "Yours faithfully"

Baroness (if Baroness in her own right)
ENVELOPE: "The Right Hon the Baroness ...." or socially "The Baroness...."
OPEN: "Madam" or socially "Dear Lady ...."
CLOSE: "Yours faithfully" or "Yours truly"

Baroness (if the wife if a Baron)
ENVELOPE: "The Right Hon the Lady ...." or socially "The Lady ...."
OPEN: "Madam" or socially "Dear Lady ..."
CLOSE: "Yours faithfully" or "Yours truly"

Baronet
ENVELOPE: "Sir [Edward Smith] Bt."
OPEN: "Sir" or socially "Dear Sir [Edward],"
CLOSE: "Yours faithfully"

Bishop
ENVELOPE: "The Right Rev the Lord Bishop of ...."
OPEN: "Dear Bishop,"
CLOSE: "Yours faithfully"

Bishops (non-English and assistant Bishops)
ENVELOPE: "The Right Rev the Bishop of ...."
OPEN: "Dear Bishop,"
CLOSE: "Yours faithfully"