邮

Right indexing radical 阝 — when on the right, this is the city-radical form of 邑 (Kangxi #163), depicting a walled settlement above a kneeling person. Marks 邮 as something to do with cities and stations: postal stations were placed at city gates and along inter-city routes. Same radical anchors 都 (capital), 部 (department), 郊 (suburb), 那 (that side).

Left component supplies the sound: 由 yóu → yóu (exact match, no shift). Adds a faint semantic match too — letters travel 'via' a postal route, exactly the directional sense of 由. Same phonetic appears in 油 yóu (oil), 抽 chōu (extract), 轴 zhóu (axis).