Invitations which come to one because of his official position are not intended for personal compliments, hence are addressed to the office, not to the man personally.
An invitation from the President of the United States is equal to a command, and may not be declined. Other engagements must be broken for it, and only grave calamity or illness should excuse one, the excuse being frankly stated instead of mere formal expressions of regret.
In ceremonious notes abbreviations should never be used.
Should one address the ruler of England, the superscription would be, "His Majesty, The King, London." The salutation would be, "Sir;" the conclusion, "I have the honor to be, Sir, Your Majesty's most obedient servant."
"His Grace the Duke of Fife" is the form of address for a Duke; "My Lord Duke" being the salutation, and "Your Grace's most obedient servant" the subscription.
In writing to the Pope of the Roman Catholic Church, one should address the letter to "His Holiness, Pope ----, Rome." The salutation should be "Your Holiness," but the conclusion remains the same form as for other dignitaries. A Cardinal of the same church is addressed "To His Eminence (Christian name) Cardinal (surname)," and greeted as "Your Eminence." Formality should be strictly observed.
An Archbishop of the Church of England is addressed, "The Most Reverend (name) His Grace the Lord Archbishop of (name of bishopric)." The salutation is "My Lord Archbishop;" the subscription, "I have the honor to be, with the highest respect, Your Grace's most humble servant." A Bishop is addressed "The Right Reverend the Lord Bishop of (name of diocese)." He is saluted "My Lord Bishop."
In the United States the Bishops of the Protestant Episcopal Church, who are not here Lords, are addressed, singly, as "The Right Reverend (Christian name and surname). D. D.," or "The Right Reverend Bishop of (name of diocese)." They are saluted, singly, "Most Reverend Sir."
The word "To" may precede a formal or ceremonious address, adding to the formality.
An envelope containing a letter or card of introduction should never be sealed, if presented in person by the party introduced. If, however, he should deliver it by messenger,--an exceptional procedure, and one not to be followed by a man except in unusual circumstances,--the envelope may be sealed.