mailbag; postal sack
Dated term for a bag used to carry mail; the modern equivalent is 郵袋 (ゆうたい).
See also: 郵袋
The postal worker set out on delivery carrying a mailbag.
diplomatic bag; diplomatic pouch
Compound of 行 (going, travel) and 嚢 (bag, sack). The exact historical derivation is uncertain, but it refers to a bag used for carrying items during travel, later specialized to mail.