料金 りょうきん後納 こうのう郵便 ゆうびんだったら
ryōkinkōnōyūbindattara

Noun
Da Copula

The "-tara" conditional form ("if/when…") of 料金後納郵便

1. If it were post-paid postage; If it were a post-paid postal service

Tara Conditional