A justice of the supreme court, a senator, a member of the house of representatives, a cabinet officer, the governor of a state, etc., all have the same formal Sir as the address and the corresponding phrase in conclusion. But there is variation in the address when the letter is of social import. The justice may be addressed My dear Justice ................., or Dear Mr. Justice ..................
The senator is addressed My dear Senator ........................ The representative in congress is addressed My dear Mr. .................
On the envelope, the forms are respectively Mr. Justice ..................., Senator ......................., Hon. .............. (for the congressman).
The social letter to a cabinet officer addresses him by name, My dear ................., and has on the envelope Hon. preceding the name and his official designation following it.
A governor is usually addressed My dear Governor ........................ And the envelope should have the title preceding the name.
In all cases except that of the President, the conclusion of a social letter is a simple form such as, I remain, Yours very sincerely.
A mayor is addressed either as Sir, or Your Honor, in formal communications, and as My dear Mayor ................. in social correspondence. The envelope properly gives him a full designation, His Honor the Mayor of ..................... The name follows, written on a lower line.
The form of address is the same for both official and social letters in the case of a Roman Catholic archbishop: Most Reverend and Dear Sir. The conclusion should run: I have the honor to remain Your obedient servant—Your, etc., being written on a lower line. The envelope carries The Most Reverend ......................., Archbishop of ...................
All letters to a cardinal begin Your Eminence. The conclusion is the same as to an archbishop. The envelope reads His Eminence Cardinal .........................