Please send the important documents by registered mail.
現金書留の封筒を郵便局で買った。
I bought a registered-cash-mail envelope at the post office.
writing down; written record; registry
Only when written 書き留め / 書留め
Refers to the act or result of noting something down or putting it on record. As a standalone noun this is less common than the verb 書き留める or the noun 記録, but It is a noun.
机の上に電話番号の書き留めが残っていた。
A written note of the phone number was left on the desk.
会議の要点の書き留めを後で見直した。
I later reviewed my written notes of the meeting's main points.
I sent the important documents by registered mail.
Just to be safe, please send this letter as registered mail.
Last week a package arrived from my parents' house by registered mail.
registered mail for sending cash
simplified registered mail; recorded delivery