A slightly lesser known verse sometimes referred to as the postal creed is a slightly altered (I am not sure how) version of a poem by Charles Eliot called Letter:
Messenger of Sympathy and Love;
Servant of Parted Friends;
Consoler of the Lonely;
Bond of the Scattered Family;
Enlarger of the Common Life;
Carrier of News and Knowledge;
Instrument of Trade and Industry;
Promoter of Mutual Acquaintance;
Of Peace and Goodwill,
Among Men and Nations.
– Charles W. Eliot