Dear Sir
When an Orthodox Jew talks to G-d he says: "Ribono Shel Olam" (Master of
the World).
When a Conservative Jew is in touch with G-d he says: "Avinu Malkeinu"
(Our Father, Our King).
A Reform Jew addresses G-d as:
"Oh L-rd, Thou art One".
A Reconstructionist says:
"To whom it may concern".