ordinary mail; regular mail
Standard postal term for non-express, non-registered mail. In computing contexts, may refer to plain data delivery without special handling.
I will send this document by ordinary mail.
It takes a few days to arrive by regular mail.
速達 is express mail, faster than 通常郵便.
書留 is registered mail, providing proof of delivery, unlike 通常郵便.
Compound of 通常 (ordinary) and 郵便 (mail).