Historical clue formulations

• Letters on a box with letters — 2021-08-28
• Post office service — 2019-03-19
• Service symbolized by a blue-and-white eagle — 2016-09-27
• Inscription on a classic letter box — 2015-03-18
• Letters in - or on - boxes — 2012-09-13
• Words below an eagle — 2012-03-17
• Label on a street-corner box — 2004-11-29
• Inscription on a letter box — 2003-11-04
• Label on a street-corner box — 2002-08-15
• Daily delivery — 1999-11-02
• FedEx alternative — 1998-08-14
• Letter box deposits — 1997-01-24
• Pony Express bundle — 1996-08-02