だい さん しゅ郵便 ゆうびん ものでしょう
daisanshuyūbimmonodeshō

Noun
Desu Copula

Expresses probability in a polite manner ("probably…") of 第三種郵便物

1. Probably third-class mail.; Probably a type of mail.

Polite
Presumptive
Conjecture