だい よん しゅ郵便 ゆうびん ものでしょう
daiyon shu yūbimmonodeshō

Noun
Desu Copula

Expresses probability in a polite manner ("probably…") of 第四種郵便物

1. Fourth-class mail.; Probably fourth-class mail.

Polite
Presumptive
Conjecture