郵便 ゆうびん私書 ししょ はこじゃありませんでした
yūbinshishowa koja arimasendeshita

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 my private mailbox.

Past/Perfective
Negative
Polite
Terminal Form