Conclusion: Believe me, truly [or most sincerely] yours, etc.
Inscription on envelope: Mr. Justice Edward D. White.
To a Senator, an official letter begins and concludes as to a vice-president.
Salutation of a social letter: My Dear Senator Lewis.
Conclusion: as given for a justice.
Inscription on envelope: Senator Hamilton Lewis or To the Hon. Hamilton Lewis.
To a Member of the House of Representatives, an official letter begins as to a senator.
Conclusion: as in the case of a vice-president.
Salutation of a social letter: My dear Mr. Clark.
Conclusion: as given for a justice.