郵便 ゆうびん私書 ししょ はこではありませんでした
yūbinshishowa kodewārimasendeshita

Noun
Desu Copula

The polite, past negative form of 郵便私書箱

1. It was not a post office box.; It wasn't a private mailbox.

Past/Perfective
Negative
Polite
Formal Register