In French, the word 'courrier' is used to refer to mail or correspondence. It can be used to describe both physical letters and electronic mail. It is a noun and is often used in the context of sending or receiving messages.
I have to send this package by mail.
In this context, 'courrier' is used to mean a system for sending letters and packages from one place to another, similar to 'mail' in English.
I'm waiting for an important mail.
Here, 'courrier' is referring to a letter or piece of mail that somebody is waiting to receive. It can be a document, a letter, or any other type of written communication sent via mail.
The mail arrives at noon every day.
In this case, 'courrier' is used in a general sense to refer to the daily delivery or collection of letters and packages.