Where does this definition of 信箱开出的挂号邮件 come from?
This entry for 信箱开出的挂号邮件 is sourced from Main Dictionary, one of the dictionaries and corpora merged into Lughet.
What is Lughet?
Lughet is a free trilingual dictionary covering nearly five million entries across Uyghur, Chinese, and English, drawn from more than ten source dictionaries and corpora.